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The Climate Frame Terrarium UPDATED

Updated: Jun 2

With natural UV-B and Infra-Red

Super-effective outdoor housing for tortoises in colder climates

Lumisol UV-B transmitting sheet on angled panels (Photo: Big Joe)

The design described here is the product of many years research, testing and development. The concept behind it was to produce a highly versatile and easy-to-adapt outdoor terrarium suitable for reptiles that could substantially reduce the reliance placed on artificial heat sources such as basking lamps in colder climates. Basking lamps have many drawbacks, including a failure to provide the ideal type of heat (water-filtered IR-A) or pattern of heat distribution (ultra-wide field) required by basking reptiles. They also consume large amounts of energy and are costly to operate and replace. The 'design spec' for this unit included maximum use of natural UV-B and the ability to provide a thermally complex microclimate optimised for reptiles.

Since the original design and concept was published by The Tortoise Trust in 2014, the subsequent 10 years have seen many thousands of keepers all over the world adapt these ideas to their own location and requirements. The great thing about this design is that it is incredibly easy to create anything from very arid desert-like environments OR true rainforest environments inside by very straightforward means. We have simplified this article to make a few things clearer and we can also confidently state that given 10 full years of use now by many, many keepers - IT WORKS!!!

In the years since we have heard from people using this method not only for various tortoises and semi-terrestrial turtles, but also for green iguanas, Uromastyx species, and bearded dragons. It can be adapted to all of them with a little ingenuity.

Let's quickly look at a pair of simultaneous measurements of ambient air temperatures taken both outside and inside one of these units:



That is a tremendous heat gain - achieved without a single watt of electrical energy being consumed. It is also incredibly 'broad band' in terms of the spectra of infra-red, UV-B, UV-A and visible lighting provided. Far superior to any artificial sources currently available.

The precise degree of gain will depend upon local weather conditions of course, especially upon cloud cover - but significant gains can be obtained even on quite overcast days. Indeed, the gains that can be achieved in these units are so high that CARE MUST BE TAKEN TO AVOID THE RISK OF FATAL OVER HEATING. In direct sunlight these units heat up very quickly - and it is absolutely VITAL that a) A shade area is provided inside the unit and b) That the tortoise can leave the unit if it needs to. This can be achieved quite easily by means of a permanently open doorway. If this is not provided, these units can, in direct sunlight, effectively turn into a 'solar oven'.

For the same reasons these units must NOT be used isolated from the mass of the ground. In other words, not elevated like a 'tortoise table' or similar. Such an installation could overheat incredibly quickly. They must be in direct contact with the soil, and there must be no other 'floor'. Tortoises need to be able to burrow into this soil to an adequate depth. If predator protection is needed, against burrowing rodents, for example, excavate a large pit first then line this with predator-proof mesh before refilling and fitting the unit directly above this.

These units are designed for use at colder times of year, as part of a comprehensive outdoor pen system and tortoises MUST be able to enter and leave them at will. In many locations the plastic film 'roof' can be replaced with a wide mesh in summer, either partially, or completely. A shaded area AND sufficiently deep burrowing facilities MUST also be provided within each unit. This is not only for essential safety reasons, but because tortoises NEED to be able to choose from a complex thermal environment - and not just be restricted to a narrow 'basking zone' or 'cool end'.

One very common misconception is that tortoises need to be warm, or even 'hot', every single day throughout their activity period. This is not only totally untrue, but is positively damaging to them.

They do get 'cool days' even in the wild. As an example, it was 33 degrees Celsius here yesterday, with bright sun, but today it is somewhat windy, very overcast, and ambient air temperatures are only just above 19 Celsius - even on 1st June in their habitat in southern Spain. By 'force heating' tortoises with heat lamps every day so that they are highly active and feeding continually, we directly contribute to over-feeding, high rates of growth, and associated metabolic bone disorders. Let them have 'quiet days' when temperatures dictate. By the same token, units like these can be configured to encourage near-natural astivation periods too. That also helps to prevent 'overdrive growth syndrome', as does a brumation (hibernation) period.

One of the very first questions that people often ask is "Will I also need a heat lamp or some extra background heating?"

There are so many variables here that it is impossible to give a definitive answer. Much depends upon the orientation of your garden or area when the unit is, the size of the unit, how much shade there is (trees, surrounding buildings) and also, of course, on your location. These units have proved highly effective even in climates such as those of Sweden, Finland, Denmark and parts of Northern Canada - so even if some additional heat input is required, it will be a lot less than would have been needed previously. In many locations you may well need nothing extra at all. In other locations some will be required. The only way to know for sure is to thoroughly test the unit at the site where it is to be used and at different times of year.

To test the unit's effectiveness you will need an infra-red non-contact thermometer to take surface temperatures of ther tortoises' carapace and plastron temperatures, plus a a reliable air-temperature thermometer to compare inside and outside ambient temperatures. Even better for this is a data-logger.

Although, just a few years ago, non-contact 'laser' thermometers like this were really quite expensive, now you can find reasonably accurate models almost anywhere at very reasonable prices! We found this one in our local Lidl! It is not quite as accurate as our professional 'Fluke' and 'Testo' models, but not too far off at all. For less than €20 there is nothing to complain about and it can teach you a lot about how tortoises thermoregulate and the safety and suitability of any habitats you use.

For Mediterranean tortoises (Testudo species) daytime air temperatures between 21-28 degrees Celsius are ideal, Overnight, temperatures can safely go much lower.

Carapace temperatures are often in the 30-34 Celsius range with active tortoises. If air temperatures exceed around 32-33 Celsius tortoises will seek retreat. Shelter for this purpose must always be provided. Tortoises will show heat stress if their body temperatures exceed around 35 celsius, and higher temperatures than that are rapidly very dangeous indeed. This is why it is so important to MEASURE and MONITOR conditions routinely.

If you are planning on adding an artificial heat source to these units, you will need to ensure that the height is sufficient to allow for adequate clearance above the tortoises (the closer heat lamps are to an animal the more problems they cause), and also to permit the use of a lamp with a sufficiently large 'beam spread' to create a adequately sized basking zone. We suggest doing a few experments yourelf first, however. You may be very surprised at just how effective these are without additional heat.

There are now a number of different REMOTE SENSING thermometers available via Ebay, AliExpress and Amazon, etc., that will connect directly to your IOS or Android 'phones (check and test accuracy, reliability and working distances carefully), but these are really useful for such setups as you can set high or low temperature alarms that notify you at once if something goes beyond the limits you have set. They can make a genuine contribution to safety. With some, you can even monitor things while you are away from home using the mobile network.

One of the many remote-sensing thermometers/hygrometers now available that can connect to your home wi-fi network and that you can monitor from anywhere in the world... accuracy and reliability does vary. Check specs and reviews carefully.

Traditional vivaria and terraria tend to offer a very limited range of temperatures, and in a very simplified, limited format: a 'hot spot' and a 'cool end'. This bears little resemblance to the complex thermal environments observed in natural habitats. It is important to stress that UV-B and Infrared are a dynamic pair, and that in order to be able to adequately utilise UV-B, reptiles need a high quality and physiologically well-matched source of Infrared in addition. Keepers have tended to concentrate on UV-B provision, while overlooking the deficiencies of Infrared provision.

This design was evolved from early trials with 'polytunnels' (sometimes known as 'hoop houses' in the US) and smaller outdoor 'cloche' systems. These were generally effective in raising body temperatures, but provision of UV-B was problematic due to the technological limitations of materials available at that time. New advances in plastics technology have now overcome this primary deficiency. In addition, these basic designs have been developed much further using data from high resolution thermal imaging systems to provide a far more 'naturalistic' range of temperature choices, and also to maximise solar energy inputs. There are a number of ways in which these units can be expanded, for example by adding additional solar-thermal collectors and thermal stores. In cold climates use of these methods can greatly expand the 'season' where outdoor maintenance remains possible.


The basic construction is quite simple, and very flexible. The base unit can consist of four walls to low-medium height, and the UV-B transmitting plastic panels are fixed via frames to a strong sub-structure. In one sense, the concept is similar to a traditional "cucumber frame". Wood and concrete blocks can both be used to create the walls.... decking board is particularly useful and weathers well. This is one of our (very) early prototypes in the early phases of construction. The base and supporting framework for the plastic sheet are clearly visible.

An early prototype during construction

When complete, that particular prototype served as a high humidity tropical house for a number of species. A combination of (non-UVB transmitting) twin-wall polycarbonate sheet and UVB transmitting panels may be used in any desired combination to produce a balance of UVB and heat conservation. This particular building was 300 square M., one of the larger units of this type we have used. It included an additional oil-fired hot-water central heating system permitting year round use, even in the winter months for delicate tropical species such as South and Central American tortoises and turtles.

Support beams for sheet roof

High humidity tropical habitat inside unit

How well does it work? Well, here's fully ripe bananas grown in Wales, UK, using this design to create a 'tropical house'.

The temperature gains in these units are incredibly impressive, and even on dull, overcast days the difference between 'inside' and 'outside' is substantial. Even better - these increases in temperature use no electricity and run up no energy bills (a real consideration these days).

These enclosure are normally best used as part of a larger 'free air' outdoor enclosure with easy access to the 'greenhouse' part. Animals should not be confined to the enclosed part only. It is critical to note that these enclosures are intended for use in cold climates and that over-heating is a serious danger if they are used incorrectly. Their purpose is to reduce reliance upon artificial light and heat and they would normally be used only at times when indoor maintenance would be employed, for example, in early Spring and Autumn/Fall. It is worth repeating that this type of enclosure can generate extremely high interior temperatures very quickly in full sunlight. It is therefore vital that there is adequate ventilation, some form of effective temperature control, and adequate internal cool retreat zones (such as a burrow). Intelligent use of 'reflectors' and 'collectors', such as black or white/silver material, also offers different ways to control internal temperatures.

A Climateframe terrarium inside a larger pen

The 'Climateframe' supports a roof of 'Lumisol' material mounted on wooden or metal frames. A partial shade zone is made from graded mesh material with some holes to replicate the kind of shade found under plant cover. This can be added to, or reduced, by simply adding or removing frame overlays containing suitable material. A cool burrow zone is also provided by means of a 'box' end with white or other reflective material on its 'roof' to reflect heat. This 'burrow zone' includes soil and stones to allow the animals to create their own cooler microclimates.

The exact amount of 'seasonal extension' that can be gained using these principles very much depends upon geographical location and the size of the unit. In general, larger units are more efficient than smaller ones. There really is no limit to the maximum size. These designs can be as large as required. Some users have reported very substantial increases in the amount of outdoor vs. indoor time achieved, from as little as less than 6 -8 weeks a year to 3.5 months. In warmer climates, up to 9 months a year can be achieved – all with near zero running costs and natural UV-B and Infrared at more than acceptable levels. To date, test units have been used with tortoises, turtles (with an interior pond), green iguanas, bearded dragons and snakes.

It is important to note that by using various basking strategies, for example, angling of the body, limb extension, and partial isolation from a cooler substrate, reptiles can substantially raise their overall body temperature above that of the ambient air temperature as long as some infra-red is present. So, it is quite typical to see body temperatures 12-15C above the ambient air temperature. In terms of these units, this can translate to:

  • External Air Temperature = 12C

  • Internal Air Temperature = 22C

  • Tortoise's Body Temperature = 33C

One of the key features is that the design is inherently flexible and may be adapted easily to suit different seasons or weather conditions. In this example, the base unit, intended for terrestrial tortoises, is covered first by removable panels with anti-predator wide mesh:

Strong anti-predator mesh over tortoise habitat

Next, modular removable panels are constructed to support the UV-B transmitting film. These can be used collectively, or singly, as required:

Modular framework in construction

Here, just one frame is in position, providing extra warmth at one end of the habitat only. In summer, frames with partial or 'dapple' shade provision can also be added or removed as necessary (all these photos (c) Big Joe):

Partial frame in use

The design consists of five principle functions:

  • Natural UV-B provision by means of new-technology thin-film plastics.

  • Natural water-filtered IR-A from sunlight.

  • The ability to offer any kind of humidity option, from arid desert-like to humid tropical, easily, in almost any environment, to suit a wide range of species. Internal ponds can also be installed.

  • A complex thermal environment with full sun, full shade, partial shade and burrowing microclimates.

  • Expandability, scaleability and minimal energy inputs.

In addition, it was essential that the design was straightforward to build, with readily available materials, and that the cost to build was as reasonable as possible. Only a design that is simple, cost-effective and versatile would prove attractive to keepers.

Natural UV-B provision

Until recently, options for making use of natural UV-B in enclosed terraria were very limited. There were a few (very expensive) types of UV-B transmitting glass and plastics available, but they were difficult to source and not necessarily easy to install and use. The main drawback, however, was cost. These materials were very expensive indeed. And being rigid, equally expensive to ship and handle. Recently, however, some new thin-film flexible UV-B transmitting plastics became available, and we spent 18 months testing them to establish their suitability for use by reptile keepers. On the face of it, they offered many advantages. They were very reasonably priced compared to rigid sheet materials, easy to handle and install without specialist tools, and appeared to offer very acceptable rates of UV-B transmission, Infrared transmission and heat retention. Two brands were trialled. Lumisol and Sunmaster. Both delivered excellent results and furthermore, withstood two seasons outdoors without visible degradation. Manufacturers of both claim a useful life of 5 years or more in general use. Given their low initial cost and ease of replacement, this is more than acceptable.

I am indebted to Frances Baines who independently tested these materials for UV-B transmission with the following results.

UV-B Transmission Properties

This may be compared to other available materials:

It is also informative to look at a simple indoor-outdoor comparison of UV-B levels where UV-B under natural sunlight are compared to simultaneous readings beneath a sheet of 'Lumisol' film. Readings were taken of both the UV Index and of microwatts per square centimeter:

UV-Index Lumisol

Microwatts Sq Cm

This may be compared with a standard type (non-UVB transmitting) horticultural plastic film, 'Tuftane':

UV-Index levels Tuftane

Tuftane UV-B

The difference is dramatic. The net result is that both Lumisol and Sunmaster provide very adequate UV-B transmission at the critical wavelengths for vitamin D-3 synthesis and as such, are of considerable importance to reptile keepers.

Both materials are easy to install either on 'hoops' as used in agricultural poly-tunnels as greenhouse replacements, or upon rigid frames, as used in our own design. It can be used alone, or in combination with other materials where structural limitations dictate, i.e., as UV-B transmitting panels in an otherwise standard structure. While the most expensive materials (UVB transmitting cast Perspex sheet) do offer technically superior performance in terms of UV-B transmission, the practical difference is relatively slight, and the levels achieved under Lumisol and Sunmaster are very acceptable indeed at the most critical wavelengths. We were able to rear juvenile Testudo graeca graeca using these materials exclusively, without any additional artificial UV-B or D3 supplementation, to bone densities equivalent to wild examples.

We are therefore quite satisfied that they are safe and effective in use. In northern climates the clear varieties, which offer maximum transmission across the full spectrum should be used for most species, though further south, or for some rainforest species, the diffuse varieties may be preferred.

A further advantage of this material when used to create an outdoor terrarium is that natural frequencies of daylight are also present, together with normal and natural UV and IR diffusion and 'scattering'. This contrasts sharply with the conditions present under artificial light and heat sources. Such 'scattered' and diffuse sources of heat and light have important implications for reptile behaviour and physiology, some of which we are only beginning to understand.

Visible light levels

Indoor terraria typically provide exceptionally poor levels of illumination. Outdoor levels measured in arid tortoise habitats are frequently 100,000 to 130,000 LUX. Indoor housing methods using ´full spectrum´ tubes are frequently well under 10,000 LUX, so barely 1/10th of natural light levels experienced by these species in the wild. This has profound effects upon behaviour, and also upon various physiological aspects such as hormone levels. By contrast, even in northern areas, the visible light levels in a ´climate frame´terraria will be many times superior to that of an indoor housing system.

Water-Filtered IR-A (WiRA)

All of these specialist films allow animals to take advantage of natural Infrared and greatly minimise (or even eliminate entirely, depending upon location) the need for artificial basking sources. This is of enormous importance to overall health and development. For a more detailed discussion, and numerous examples, of this topic see our earlier report into the health effects of basking lamps on reptiles (updated version of that report will be available on this website soon).

The use of these new plastics permits not only natural UV-B usage, but critically, allows this in combination with natural wavelengths and patterns of Infrared use.

The results speak for themselves. There is no discernible difference between patterns of natural (outdoor) infra-red in reptiles and the patterns observed using thermal imaging cameras of infrared use under these films. By comparison to the patterns observed under artificial basking lamps the results can only be described as dramatic. There is 'deep' and very even heating, even to the extremities and the unnatural surface heating seen with typical artificial sources is entirely absent. It should also be noted that the 'dehydrating' effect of typical basing lamps is also entirely eliminated. This is immediately obvious when comparing results from a thermal imaging camera.

The very even heating effect of natural Infra-Red upon the carapace.

Unlike the uneven heating effect of heat lamps, the warmth of natural infra-red penetrates much more evenly right through the full depth of the body. Even the plastron is evenly heated.

Note the particularly even heat, right to the plastron and extremities. Subjectively, the entire animal feels like a 'hot rock', which is exactly how they feel after basking in the wild. The 'top to bottom' even heating pattern is very evident here.

By comparison, under artificial basking lamps there is a strong tendency for very uneven heating, with 'hot spots' in areas closest to the lamp, which much of the rest of the tortoise remains too cold - especially the plastron.

One effect of this is that tortoises will often bask for too long, in a vain attempt to gain sufficient core body temperature, while the area closest to the lamp not only overheats to the point where burns can occur, but the entire tortoise is subjeced to the extreme drying effects of such heat sources. This has profoundly negative effects upon both behaviour and their general physiology.

Humidity control

Different species require very different levels of ambient humidity. In captivity, many keepers have tried to 'overcompensate' for the severe drying effects of artificial lamps by providing completely unnatural elevated levels of humidity using 'moist hides'. This exposes the animal to sustained levels of humidity that it may never experience in nature, and this is not without consequences. One particular effect is over-softening of the keratin and an increase in susceptibility to bacterial and fungal pathogens. This author has always maintained that it is far better to provide a truly suitable environment in the first place than to attempt to 'fix it' using artificial and potentially risky methods such as this. As to what constitutes a 'suitable environment' for any given species, the point of reference for this should be reliable data from the environment in which the species inhabits in nature. It is of course extremely important that this understanding is based upon genuine, reliable data and not upon ill-informed guesswork.

If a truly suitable environment is provided, there is no need to provide completely artificial and extreme measures to compensate for inherent defects caused by poor design elements elsewhere in the habitat.

Humidity is primarily controlled by means of airflow restriction and by the amount of water added to the enclosure. High rates of airflow with little additional water will soon result in an arid environment, while lower rates of airflow with larger amounts of added water will rapidly cause a rise in ambient humidity. This is absolutely no different from the methods employed in agricultural greenhouses.

To obtain a correct or desired level of ambient humidity at any given temperature it is simply necessary to balance the rates of airflow and water inputs. By this means, it is relatively simple to create a wide range of humidity levels, either on a constant or upon a cyclic basis.

Passive side vents

These are used to control temperature, humidity, or both.

Open-mesh passive side-vents (Photo: Big Joe)

Various means may be employed to add water (their suitability depending upon the species being maintained) but electronic 'self-watering' irrigation systems, misters and sprayers can all provide useful options. These can range from simple to more complex, with timers and 'electronic leaf' type sensors being used to carefully create and control almost any type of microclimate.

Our own trials mainly concentrated upon use for arid habitat dwellers. It should be noted that with larger, more agile species some form of physical protection for the UV-B film is invariably required. This can be achieved using metal twin-weld mesh on a sub-frame, or a stronngplastic alternative. This will prevent contact, tearing and escapes. UV-B loss is minimal with medium-wide meshes. Very fine mesh will of course block substantially more UV-B. According to figures provided by Frances Baines typical chicken wire blocked 7% of UV-B, while 1/4” twin-weld mesh blocked 35-37% of UV-B. It is advisable therefore, to use as wide a mesh as possible, consistent with preventing damage or escapes. The more the total surface area of the wire used, the more UV-B will be blocked. Of course, some species may require no such protective measures in the first place.

Units employing the UVB transmitting film were tested at various locations from Southern Spain to Scandinavia. In all cases significant gains over ambient were recorded. Air temperatures within and outside the units were compared, and in addition, body temperatures of tortoises inside the unit were monitored. As the units were tested under a very wide range of conditions, at various latitudes, and the sizes of the units on test varied considerably, it is impossible to provide too many specifics, but examples of ambient air temperature comparisons include:


  • Ambient: 9C

  • Inside unit: 20C

  • Gain: 11C


  1. Ambient: 8C

  2. Inside unit: 18C

  3. Gain: 10C


  • Ambient: 13C

  • Inside unit: 25C

  • Gain: 12C

Canterbury (Kent)

  • Ambient: 17C

  • Inside unit: 31C

  • Gain: 14C

A general overview of measurements taken suggests that an air temperature gain between 10C to 15C would be typical in early Spring in moderate or somewhat cloudy conditions. Temperatures do of course vary hour by hour, and there are other variables such as time of year, cloud cover and orientation of the units to the sun. This is a typical report compiled by one of our beta-testers in Sweden:

“Sunday 18th May 11:00, Västerås, Sweden

Weather: sun

  • Outside temp 17°

  • Inside temp. 27°

Tortoise temperatures (T g. ibera)

Carapace. 32°

Plastron 29°

Tortoise two

Carapace 29°

Plastron. 24° “

The key point is that in all cases very substantial increases of both ambient air temperature inside the units, together with significant increases in both carapace and plastron temperature are experienced over conditions and body temperatures outside of the units, and that this is achieved with no additional energy inputs. No basking lamps were used, and no artificial background heating employed.

The basic design of these units can be extended. It is entirely possible to add additional solar collectors and accumulators to save heat during the day, to provide additional heat at night – although with many species low temperatures at night may not only be normal, but beneficial. The need for this (or for supplementary artificial overnight heat) is entirely dependent upon the species concerned. It may not be required at all for temperate species in some locations, while tropical species will almost certainly require it. In any event, such need will be considerably reduced over typical methods of maintenance as a significant proportion of total heat requirements will be met from solar resources.

It is extremely important to understand that smaller units, by themselves, will not 'hold' heat to anything like the same degree as larger units. In this respect, the larger and the greater the volume and mass of the unit, the more heat will be retained and for longer periods and the more minute-to-minute variations will be stabilised or 'evened out'.

Over the past 30 years we have used similar designs of housing from a few meters square up to structures 30M X 12M, and in every case, the larger units performed the best, however, even the smaller units offered considerable improvements in temperature compared to what could be achieved without them. These design concepts are very flexible, and can be easily adapted to different locations and situations. We have created near desert condition in wet and windy Wales, UK, and humid tropical conditions in the semi-deserts of Southern Spain… it really is as straightforward as understanding the principles involved and applying them imaginatively.

The new UV-B transmitting flexible plastic sheet in combination with these designs is capable of transforming our expectations of how to keep tortoises in captivity. Few would dispute that where possible, some form of outdoor maintenance is best – and these designs and concepts greatly extend what is possible, even in colder, challenging climates. The less we have to rely on artificial light and heat sources the better too, not only for the animals subjected to them, but also from the point of view of our own environment. This takes us much closer to a genuinely 'naturalistic' method of husbandry using the best possible light and heat source out there for reptiles – the sun itself.

There are few limits to this method. By all means, experiment and let us know (and see) your results. Some great setups can be created. Your tortoises will thank you for it.

Thanks and acknowledgements

Special thanks to all our followers and supporters for testing various components of this design and for collecting very important data from such a wide range of climates and locations. Thanks also to Frances Baines for her comments, support and diligent testing of the UV-B properties of materials.

This design is based upon original work carried out by A. C. Highfield and the Tortoise Trust. (c) Tortoise Trust 2014-2024

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1 ความคิดเห็น

This is so interesting. Thank you. It is beyond my DIY scope however- Are there any plans to manufacture and sell these ( in uk!)

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