Sitting room unbearably chilly after - what? building work ?

[DaturaDream]

In the course of last year I had a south west facing extension built on the back of my Victorian cottage. At the same the builders knocked down a 60's porch on the front of the house, relocated the front door and used what had been the porch space to extend the front sitting room with a square bay window.

All sounds good, but it used to be cosy and now it's FREEZING!!

In the old part of the room I have plugged the gaps between the skirting boards and the floorboards with draughtex and will do the caulking next. Yes the floorboards themselves are draughty but no worse than they were before and anyway there are loads of rugs on the floor. In the new bay window part the floorboards are laid on screed so no draughts coming through.

I bought one of those thermal leak detectors and as far as I can make out today the skirting board gaps are now consistently at 11 ish degrees.

The walls of the old part of the sitting room are all 12 something and the walls and ceiling of the new bay window are just 11 something.

So disappointing as I thought new building regs etc would mean the newly built bits were much better insulated than they used to be so it would be warmer than before. At the moment the temperature in the sitting room is 14.2 and here in the kitchen where it hasn't even been sunny today it's 17.8.

The builder assures me the bay window is all properly insulated and blames the floorboards. So why would the room be colder than before? I dread putting on the heating and finding I can't get it warm. Thanks in advance for any clues as to how to proceed.

We had a very similar situation and ended up resorting to laying carpets on our beautiful original wooden floor, although in your situation i would be inclined to think that the new build is not properly insulated? - hopefully someone more knowledgeable will be along shortly to advise!

Our bay is original 1930s but those rooms are much colder than the ones without the bay - and the bay part noticeably colder than the rest of the room. In our case though I assume it’s lack of insulation plus the additional external wall (& aren’t bays often single skin?).

I never noticed the same in our old Victorian terrace with a bay though.

Hope you manage to get it sorted.

I've just realized the skirting board gaps may still be draughty - I poked the draughtex in but haven't yet caulked them. See my amazing builder vocabulary. Could the caulking be critical?

Plus I should have said the skirting board is not the original one, which had to be taken off by the floor sander. You can clearly see the gaps between the new skirting board and some floorboards.

Thanks for the replies guys. I'm
hoping the problem is the skirting boards and not a single skinned bay sdaisy26!

Yes an awful lot of heat can disappear under the skirting boards. We had our builder go around them with caulk the same colour as the skirting board and the difference is unbelievable. We also used to get a sort of damp winter air smell from under the house and it’s solved that issue too.

Yes you're so right johnnyutah - before I did the Draughtex there was a kind of earthy smell. Right so I'll stop watching YouTube videos of caulking and eeek actually try doing it

TBH caulk can be a really, really messy job and as it dries quickly it’s easy to make a mess. I think I paid all of £150 for the whole flat to be done by a builder. Took him an hour and the result was so much better than I could ever do.

Thanks johnnyutah I'm glad to hear that. I'll do the same.

I've belatedly realized that logically if it was just the insulation of the bay that was the problem, the room temperature would be no different from outside. But as the room
Is significantly cooler than outside (yesterday 15 vs 18) the cold air must be coming from under the house.

So I know what to do now! Thanks all