There is no standard measurement for the thickness of a garden room wall. The final measurement varies between companies, the size of the building, the structural build-up chosen and the thermal performance target.
Some garden room companies build their rooms to the same specification as a modern timber frame house. The multiple layers in this build-up create thick walls of around 150-250mm, but on occasion, we have seen walls as thick as 300mm used. Other companies have created a pared-down version that produces a finished wall around 70-100mm thick.
With the house quality build-ups, the garden room designers create a structurally strong, highly insulated building envelope. The insulation levels allow them to meet and often exceed the U-values for new houses set out in the Building Regulations. So, your room will be easy to keep warm and cost-effective to heat and cool.
With the thinner wall build-ups, the designers focus on material efficiency, speed of installation, and keeping their prices competitive. Another bonus is that with the thinner wall sections, you end up with more useable space within your room than with the thick wall build-ups.
From the outside, garden rooms might look the same, but under the cladding, they are all different
Spend a few minutes online looking at garden room designs, and you could be forgiven for thinking that some companies' rooms look just like those of other companies; the only difference is the price tag.
If you could x-ray the designs and look under the external cladding, you would quickly realise that the wall structure is very different between companies and price tags. If you were to compare specification lists on various sites, you would see the same layers of material listed, for instance, Structural Insulated Panels (SIP's), breather membrane, Cedar cladding etc. The thing is that there is often no mention of how thick the overall wall is, so you know if you are comparing like with like when researching your options.
SIP's are commonly quoted on specifications, but they are not all the same
We have mocked up some examples of SIP's garden room build-ups that we commonly see. They would all be listed on a specification as SIP's structures, but as you can hopefully see, the implementation varies, as does the final wall thickness.
Some garden room companies use the same thick SIP panels as are used in housebuilding; they couple these panels with membranes, air spaces, service voids and interior and exterior finishes. This creates a thick wall of around 250mm, as in example D in our graphic.
Other companies use this same multi-layer build-up but utilise a narrower SIP, as we can see in example C. Then there are companies that utilise one leaf of the SIP panel as the internal finish; this creates a thinner wall profile again, as we can see in example B.
Then, there are a few designs where the SIP panel also forms the internal and external finishes, as we can see in example A.
Insulated timber frame build-ups also come in various thicknesses
Some garden room designers prefer to use traditional timber frames for their core structure, with insulation slotted between the framework. Like SIP's, the overall thickness of an insulated timber frame wall varies between companies.
The thickness of the timbers used for the framework varies greatly between companies. Some use 50mm thick timbers and others 100mm timbers, but some companies go as far as 200mm thick timbers. The thicker the timber, the stronger the framework will be.
While creating a stronger structure, the thicker timbers also allow for more insulation to be installed.
The following image shows two typical insulated timber frame build-ups. Example B is 170mm thick and includes a layer of sheathing board fitted to the exterior side of the framework. This layer increases the strength of the frame.
In example A, the completed wall is just over 100mm thick but doesn't include the sheathing layer like in example B. Some designers omit this layer to keep costs down.
Thinner walls = more internal space + often cheaper to buy
Thicker walls = greater strength + more insulation + cost-efficient to run
Look at this graphic; we modelled up the same size room with the same furniture arrangement to showcase how the thinner walls offer greater internal space. The first room has 100mm thick walls and the second 250mm thick walls.
The first option has more useable space inside and will cost less than the second example as it is more material-efficient and would be quicker to build. The second option has a more robust core structure and will be more efficient to heat and cool, so it will cost less to run in the long term.
Look at the two rooms from the outside, and they look exactly the same, but as we can see, their core structures and the amount of insulation included differs greatly.
A telltale sign of how thick a garden rooms wall is...
Even without reading a garden room's specification, there is a telltale sign of how thick the walls are. If you explore a gallery of photos on suppliers' websites, just look at the window and door reveals - do they have them? On models with thinner walls, the inside of the door or window frame is typically flush with the wall's face; there is no space for a window sill.
In a garden room with thicker walls, the window or door frame would be recessed into the wall, and there would be a window sill for putting a plant or other objects on.
Delve deeper, so you know what you are buying
We will not finish this post by saying you should be buying a garden room with X thickness walls. However, we want to encourage you to delve deeper when comparing your options so that you know the structure you are buying.
When comparing companies that appear to offer similar style garden rooms, read the specification carefully, and if it doesn't make it clear how thick the walls are, ask them to explain their build-up.
A garden room is a big-ticket purchase with a long lifespan; we want to make sure you are fully informed about what you are buying.