In timber framed construction the walls are usually insulated on the inside. If this is the case then you must consider the build up of moisture and condensation inside the internal walls, which may happen if you don’t use the correct vapour barrier.
Without a barrier warm moist air from our bodies and breath will travel through the building and the permeable insulation eventually hitting the cold surface of the exterior. As it hits the cold surface it condenses and forms water. Moisture left to ‘sit’ without drying out will eventually form mould and damp and in the worst case scenario, rot.
To put it in its simplest form it’s the same effect as the outside of a cold beer glass when water collects on the outside of the glass.
If you don’t use a vapour barrier the inside of your garden room is like the beer glass.
A vapour barrier keeps the moisture on the inside of the building.
This process only happens however when the insulation is permeable such as wool or mineral wool. If foil backed insulation is used then it is recommended that all the joints be taped with a foil insulation tape as the foil itself acts as a vapour barrier. The issue with the foil tapes often used in UK construction is that they don’t adhere that well to anything other than the foil board, the tape often lifts and allows moisture vapor into the walls around the joints. As a precaution it is recommended that a vapour barrier is used as well as foil backed insulation.
The issues with vapour barriers and foil backed foam insulations are that they are not the most environmentally friendly materials. Vapour barriers are essentially big sheets of plastic and foam backed insulation uses a lot of hydrocarbons in its manufacture. It also adds to the cost of any construction process.
Here at Spacetwo our solid log buildings need no additional insulation in the walls because the wood itself has excellent insulation properties and is 100% permeable so any internal moisture is naturally dispersed through the wood fibers and therefore no vapour barriers need to be used. Our roofing system is a warm roof construction so all the insulation is on the outside of the building and therefore will not get any condensation vapour in the roof void.