How can I fix a cold and damp extension room?

Question

We recently bought our first house, a rather old 3-bed terraced house. The adjacent house has been empty for 4 years. The 3rd bedroom in my house is a single room extension I'm using as an office and it's always cold. We didn't get a survey (inspection). Our agent told me the house to his knowledge has never failed a survey. We did have specialists (contractors) evaluate & quote for free so have had full electrical safety check, roof inspection, damp inspection in extension & ground floor.

I've pushed some insulation into the corners of the roof/ceiling (slanted roof). There is a small plastic vent in the top of the room which says "do not cover." I've put glue along the PVC window frame as there were some holes in the paint and I wondered if this was creating a draft. When the heat is on, the rest of the house will be warm but when it cycles off within an hour my hands are numb. The wall next to the empty house in the extension sounds real hollow when I knock on it. We already had to damp-proof the ground floor wall on the empty house side as we had rising damp in that wall

Whilst in the attic I noticed on the back wall there are gaps in the mortar through which you can see outside. The bricks are very black where the wall ends between our attic and the empty house and some crumbled bricks have fallen out of an inner partial layer of bricks. Some bricks seemed a bit damaged. It's also possible to get around the end wall into the neighbouring attic (which isn't very well insulated) and obviously that house isn't being heated whilst vacant. Some of the beams have mould, and the roofer who came over had a look and said it will dry out after roof repair.

Should I replace and re-mortar the bricks? Could the empty neighbouring house be causing some of our insulation issues? If so, should I put up some kind of barrier or cover the gap between the walls of the attic, or are they supposed to have a gap between them? And is there a cheap way of making the extension warmer?

Answer 1

It sounds like you have at least two problems that contribute to the warmth (or lack of warmth) of a room.

First, this extension room needs to be connected to your heating system and it's unclear from the description whether this is the case. Older homes (based on spelling I'm guessing you're in the UK) probably have a boiler and radiator system, so you should have a radiator in this room (and place one there, if there isn't one yet).

Second, this room does not have a proper envelope - the brickwork, vapor barrier, insulation and finishing that helps houses keep the climate inside different than outside.

(Image taken from short video https://youtu.be/8VLX_dqybpA)

From the outside to the inside, this wall has bricks, an insect screen (optional), a damp drainage mat, house wrap, then metal studs with insulation between, then gypsum board for the wall surface. If there are holes in your bricks and mortar, those should be patched first before upgrading the wall insulation. All walls and the ceiling and roof of your extension need to be properly built and insulated, including the shared wall adjacent to the vacant house.

You can seek out an insulation contractor with a thermal camera, they will be able to pinpoint the spots in the wall and ceiling that need addressed because they show a different color on a thermal image. Such a contractor should also be able to recommend a type and R-value of insulation for your specific situation.