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Hi DIY experts, calling for your collective wisdom.
I am having a timber cabin installed at the end of our garden in the spring. The cabin suppliers will install the cabin itself. I will do the first fit, by constructing a suspended timber base and insulating it.
I have designed the timber base in (I think) a pretty standard way: Timber joists running the longest span (left to right), raised off the ground using threaded bars, all adjusted to be perfectly level and square. I could use timber posts for this, but threaded bars would have longer life with no rotting. I will fit PIR insulation (around 100mm) between the joists, with all joints covered with alu-foil tape so as to create a vapour barrier and air tightness.
Here comes the issue: instead of building up the cabin directly from the base I make, they insist on raising the building on their own bearers, just as you would builda cabin if you were working from a concrete base. This would then leave multiple voids between my insulated base and the finished floor of the cabin. These voids are sealed off as the cabin walls fix into the base itself, so no 'outside' air or gusts of win can get in (leaving no ventilation either~).
My options:
I am having a timber cabin installed at the end of our garden in the spring. The cabin suppliers will install the cabin itself. I will do the first fit, by constructing a suspended timber base and insulating it.
I have designed the timber base in (I think) a pretty standard way: Timber joists running the longest span (left to right), raised off the ground using threaded bars, all adjusted to be perfectly level and square. I could use timber posts for this, but threaded bars would have longer life with no rotting. I will fit PIR insulation (around 100mm) between the joists, with all joints covered with alu-foil tape so as to create a vapour barrier and air tightness.
Here comes the issue: instead of building up the cabin directly from the base I make, they insist on raising the building on their own bearers, just as you would builda cabin if you were working from a concrete base. This would then leave multiple voids between my insulated base and the finished floor of the cabin. These voids are sealed off as the cabin walls fix into the base itself, so no 'outside' air or gusts of win can get in (leaving no ventilation either~).
My options:
- I do nothing. Accept that some cold air will travel between the insulated base and the finished floor - at best it may just be a little colder, at worst this could cause damp since warm air will meet cold air?.
- I ask the installers to leave the floor boards up. I can then fit an additional layer of PIR insulation in between, adding to the 100mm already below. All voids would be filled but it would be a bit of a criss-cross of PIR running in different directions and far from air tight?
- I ask the cabin installers to avoid using bearers altogether, and build directly onto my base (thus solving all my issues in one easy way, this is obviously my preference)
- Or an alternative that i've not actyually thought of myself! ...putting down some kind of airtight permeable membrane?