Insulated Garden Office or a Garden Room

This article is a part of our English Knowledge Base

05.02.2016
Author: Risto Alt

Read this quick and easy guide for information on how to insulate a garden log cabin quickly, easily and inexpensively!

Log cabins are the most affordable garden buildings you can possibly find on this planet Earth and most of them are quick and easy to install yourself or using professional services. The assembly of an average log cabin sized 8-15 m2 takes no more than 2-3 days.

A basic garden log cabin is a seasonal building, but with a very small amount of extra work and a little spending you can insulate your cabin and use the space 365 days a year.

One of the best materials to use for the insulation is a glass fibre mineral wool, available in rolls, panels or slabs.  An additional layer of polyamide membrane designed for timber frame construction will increase air tightness and resistance to UV light. This intelligent material alters its structure depending on relative humidity. These two coatings are almost all you need for a proper insulation!

There are four main areas that must be insulated: roof, floor, walls as well as door- and window frame joints.

Start with the floor insulation. The best foundation type for an insulated cabin is a concrete base. First of all you need to build up your cabin, finish the roof and attach the roofing felt, then you can be sure that a sudden downpour will not interrupt the insulation and spoil the wool and floor boards. For the same reason leaving the floor boards last to install is a smart choice even if you are not going to insulate your log cabin.

Floor insulation

After the cabin has been installed, but before laying down the floor boards it is time to insulate the floor. Insulation is laid between the foundation beams and using rigid or semi-rigid mineral wool panels is a good choice. These panels combine insulation and a wind barrier for floors.  Measure the distance between the foundation beams and cut appropriately sized panels by using knife. These panels must not be in direct contact with a ground to avoid moisture ingress and ensure a good ventilation beneath the cabin, which is crucial. Commonly used foundation beam thicknesses are between 4 and 10 cm, depending on the size of the cabin and a producer. One simple way to lift the wool panels up off the ground is to lay 1-5 cm (depending on the thickness of the foundation beams and base) high laths on the ground between the foundation beams and then you can place the wool panels on them. Cover the floor with polyamide membrane film for an additional wind protection and install the floor boards.

How to insulate garden room floor

For example, most of our medium sized garden log cabins have 4,4 cm thick foundation beams. In that case we recommend using 1,5 cm thick laths and 3 cm wool panels (these panels are available from thin 2 cm thickness up to 10 cm), so that the panels will be levelled with the foundation beams and then lay down the membrane. If the outside temperature does not drop significantly lower than 0 degrees Celsius, 3 cm wool panels together with membrane will do the job.

Roof insulation

Now that the floor has been insulated, it is time to take care of the roof from the inside (ceiling). For the prefect result it is also very important to use high quality roof shingles on the roof to protect the roof boards from the outside elements, keeping them moisture free and making them windproof. Only proper roofing felt and shingles on the outside together with fine insulation on the inside ensure a weather-resistant, warm and windproof result.  40% of the warmth exits through the roof, so this is how important it is to have your roof well insulated and covered.

How to insulate garden room roof

The first step is to measure the thickness of roof bars (purlins) to buy corresponding glass mineral wool. Wool thickness must match the thickness of purlins or exceed it slightly (2-3%), but in no way thinner than the purlins.

For example, the roof bars of most of our log cabins are 15 cm thick. In that case you can go for glass mineral wool rolls or panels with the appropriate thickness around 15-15,5 cm. Now measure the distance between the bars and cut appropriate sized pieces of wool. Dimensions of the insulation should be slightly (1-3%) larger than the exact distance between the purlins to fill the entire insulated cavity and stick the wool between the bars without any fixings.

All that said and done, add polyamide membrane coating or similar for an additional insulation and do the internal cladding. The choice of available cladding materials is wide, you can use wooden boards, wooden panels, plywood sheets, OSB and the list goes on.

Wall insulation

By now, the floor and roof of your garden building have been insulated and it is time to switch to walls.

Glass mineral wool in rolls or slabs is a great material to use. Start with vertical wall joists. If you are going to use 5 cm thick wool then you should use 5 cm thick timber joist, or if your local climate demands 10 cm wool insulation then the bars and mineral wool panel must be accordingly 10 cm thick. For the weather conditions in most parts of England, Germany, Austria and Switzerland 5 cm thick insulation is more than enough. In some parts it is well enough to insulate roof and floor only.

How to insulate garden room wall

Common width of wool rolls and panels is around 50-60 cm. Before you start installing the wall bars, check the width of your glass mineral wool rolls or panels.

Distance between the joists must be slightly less than the dimensions of the insulation. That will ensure that the insulation stands still between the joists and all the insulating cavity is properly filled. Now cover the walls with the membrane. For the cladding of walls you can go for wooden boards, wooden panels, plywood sheets, OSB or any other material on your preference.

Last step, insulate the door- and window frame joints. We recommend water-repellent glass wool strips or similar. Usually the distance between the frames and walls is around 1 cm on the sides and 4 cm on the top. You may know that wood is a natural material, growing and adapting depending on the temperature, humidity and other weather conditions, especially during the first 6-12 months after the assembly. That is why you must not fill the cavity tight, to leave free space for the wood to adapt. During these first months you may have to adjust the doors and windows a few times to keep them functioning well. So fill the cavity, don’t do it tight and finally attach the boards.

And that will do it! Your garden room or home office is now well insulated. It is time to coat your cabin with wood preservative from the outside and take care of the internal decorations and off you go with your all year round use garden building.

We thank Isover Saint Gobain for all the cooperation and help in creating these insulating instructions!