Best way to insulate porch / roof void connected to house – thermal envelope & condensation risk - Heat Insulation

January 5Jan 5

Hi all,

I’m after some advice on the best way to insulate a porch at the front of my house.

The porch is single storey, with an ensuite bathroom directly above it. I’ve taken the porch ceiling down, which has revealed that a few voids are currently all connected, which doesn’t feel ideal from a thermal or condensation point of view.

At the moment:

The void above the porch is connected to a cold, ventilated roof void at the front of the house
That space is also connected to the sub-floor void under the first floor
The soil stack from the ensuite passes through this area and continues up into the main loft, which is also cold and ventilated
There’s little to no insulation under the ensuite floor, and services run through the void

So there’s a clear path for warm air from the house to reach cold spaces, and I’m concerned this is effectively breaching the thermal envelope and increasing condensation risk around services.

I can see two main ways of tackling it:

Option 1: Close off the cold roof void where it connects to the porch (it’s actually a fairly small triangular section) and bring the porch and void above it into the thermal envelope. Also worth insulating under ensuite floor?
Option 2: Leave the porch cold and insulate at the interface with the house, including insulating under the ensuite floor and carefully sealing around the soil stack and other services.

My current thinking is that Option 1 may actually be less work overall, as the warm–cold connection is small and well defined, whereas Option 2 would involve a lot of careful airtight detailing around services. That said, I’m very conscious of condensation risk, particularly with the soil stack passing through into a cold loft, so I don’t want to create new problems.

Any advice would be greatly appreciated. This house is the gift that keeps on giving 🙃