Log cabins need damp proof membranes! There are many companies selling log cabins, but very few that provide a damp proof membrane (DPM) for their cabins. Nor even advise customers about this.
There are a few main reasons why cabins don’t last as long as they should do. The major one being the lack of a DPM which prevents damp rising up into the base timbers. Then it progresses up further into the cabin floor an wall logs……. “The bearers are pressure treated, so it doesn’t need one” – WRONG! The base timbers will eventually rot, even if treated. The base timbers will transfer this moisture up into the floor boards and bottom wall boards. Such a shame to have to replace a cabin when just a few extra pounds would eliminate this problem from the outset. Installing log cabins correctly saves years of heart-ache later on, simple as that!
Correctly installing DPM is essential
So laying a DPM is essential in our view, but it’s also how it’s laid that also makes a big difference. Cutting it off around the edge of the floor / bearers just exposes open edges at ground level. Therefore rain / rain water will get on top of it and run in under the building. With nowhere to go because the DPM is waterproof! Even worse if there’s a dip in the base. This will cause a puddle under the floor. Then the water could evaporate creating a high air moisture content, which will rise up through the floor. The last stage is what causes the damage. It transfers into the building where it will condense on any colder surface. This “water” looks like there is a leak (especially if it condenses on the underside of the roof).
This is not fantasy, we have seen this actually happen. This could also happen if the bearers are just laid on strips of damp proof course. Although not as likely, assuming the ends of the bearers are open and will therefore ventilate.
The best way to lay a DPM is if it is over-size and then laying the bearers on top of it. Crucially the excess DPM is folded back on top of the bearers before building the walls. This way there are no cut edges at ground level, ensuring it stays dry. Our DPM kit also adapts the floor to include an extra timber cover fillet all around the edges. This covers the exposed DPM, Thus protecting it from UV degradation and also mechanical damage (strimmers etc)…..
If you have an insulated floor, then the spaces between the bearers is full of insulation. Hence there are no air gaps and therefore nothing to ventilate (warm deck). If it is not an insulated floors then the spaces between the bearers need ventilation. This can be easily achieved by drilling a series of holes along the appropriate flank. Drill these with an upward angle at least 30mm up from the bottom so if any water does find it’s way to the opening, it will simply run back out again.
These damp proof membranes for log cabins measures will probably at least double the life of your cabin. Easy when you follow the correct installation method, and only a few pounds extra.