Heat loss in new rooms

Soldato
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27 Mar 2013
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I realise this is a bit of a finger in the wind type question, but here goes. We have had a single storey extension finished recently ~2 to 3 months ago. I notice that it's losing around 5-6 degrees overnight. Is this normal? The heating is a 1kw rad in each room with 1 being 2.5m X 3.5m and the other 2m X 2.5m. the bigger room does have a window in that's about 1.8m wide, and both are essentially 2 outside walls. It's an apex roof rather than a flat roof. There is insulation in there, but not as much as I would have expected, think about 6-10 inches or so (I remember it being the thickness of the joists and they were about that). The loss is from when the heating clicks off at 10pm and it clicks on at 5 am. The drop is from 20ish to 14ish.
 
Soldato
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What isolation was used? Was it the celotex foam stuff with the foil front and back? Would you say it was 100mm thick or more?

Also, did you notice if any of the same stuff was put in the floor?

What do you have on the floor? Tiles or carpet?

The insulation in the joists is likely to only be 100mm thick as there needs to be a gap between the roofing felt/finish and the insulation for air flow.

Do you have ceiling joists or is it a vaulted ceiling? Are you sure that insulation was put in the outside wall cavities?

That sort of temperature drop in a new extension is quite alot in my opinion.

Do you know if the building inspector came round and if so how often?
 
Soldato
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insulated double walls in the extension construction?
did they do underfloor insulation?
are doors kept closed at night to prevent the flow of air through rooms from drafts?
have the windows been properly sealed, can you see them sealed around the outside?

for stupid comparison, the drop seems rather high, as an outdoor hot tub will lose similar on a cold night.
 
Soldato
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Glebe Park
Providing all your uvalues are met in the floor, walls, roof and windows and everything has been met in terms of the regulations then things would point towards any heat that has built up to those rooms is probably being leaked through the existing part of the house.

As a comparison the temperature drop you're seeing is on a par with my 1970s ex council house with blockwork cavity walls with a 25mm posting internally with rockwool insulation between and I'm pretty stingy with my heating! Its something I've never understood whenever I've been doing extensions / uvalues. What's the point in super insulating an extension when all the heat is just going to find its way out through the leaky old part of the building anyway. Unless there is a decent seal / divide between the old and the new.
 
Soldato
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What isolation was used? Was it the celotex foam stuff with the foil front and back? Would you say it was 100mm thick or more?
It was the foiled stuff thats in the walls, think it was about 100mm.

Also, did you notice if any of the same stuff was put in the floor?
Yes there is some insulation there, not sure exactly what type, but its a good 10 inches drop to the concrete in the garage (both rooms are concrete floor as well).

What do you have on the floor? Tiles or carpet?
Laminate, which does feel cold, but one rooms a utility and one is a study with roller chair so not much choice.

The insulation in the joists is likely to only be 100mm thick as there needs to be a gap between the roofing felt/finish and the insulation for air flow.
Its not vaulted, imagine a typical ceiling upstairs i.e. flat inside, but with an apex for the loft.

Do you have ceiling joists or is it a vaulted ceiling? Are you sure that insulation was put in the outside wall cavities?
Think it was the rolled stuff thats above the ceiling.

That sort of temperature drop in a new extension is quite alot in my opinion.

Do you know if the building inspector came round and if so how often?
He came round 3 or 4 times, but not sure how much interest he took in it, could have just been a cursory glance.

insulated double walls in the extension construction?
did they do underfloor insulation?
are doors kept closed at night to prevent the flow of air through rooms from drafts?
have the windows been properly sealed, can you see them sealed around the outside?
Brick and breeze, with a cavity with insulation in (see above), internal doors are left open (apart from the wall into the garage as its freezing in there). The windows are sealed, as i noticed they werent originally and got him back in:D.

for stupid comparison, the drop seems rather high, as an outdoor hot tub will lose similar on a cold night.

Providing all your uvalues are met in the floor, walls, roof and windows and everything has been met in terms of the regulations then things would point towards any heat that has built up to those rooms is probably being leaked through the existing part of the house.

As a comparison the temperature drop you're seeing is on a par with my 1970s ex council house with blockwork cavity walls with a 25mm posting internally with rockwool insulation between and I'm pretty stingy with my heating! Its something I've never understood whenever I've been doing extensions / uvalues. What's the point in super insulating an extension when all the heat is just going to find its way out through the leaky old part of the building anyway. Unless there is a decent seal / divide between the old and the new.

Window vents open?

I did check the vents first:p. Ive (hopefully) stuck the planning picture in. The utility part is part of the old garage (although an interior wall and insulation were added). Also theres no heating in the 'hall area' just the lounge, kitchen, dining area, study and utility. Also the new front door is a rockdoor, but it does feel cool in that area, so might try with the study door shut tonight to see if thats the difference. I'm not sure if a hot tub can be compared, theres a massive amount of thermal mass at play there.

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Soldato
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It is possible that parts of still drying out, and as such isn't set, and will improve over time.
Once everything 'warms'.
 
Soldato
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He came round 3 or 4 times, but not sure how much interest he took in it, could have just been a cursory glance.


Well it all sounds like it's been done correctly if all the above is as you say. The building inspector should be doing his job correctly as at worst he would lose his job if he overlooks the regs. It looks like they don't do alot but they are normally pretty good as they know what to look for at each stage that they come and inspect the build.

You could try to get a second opinion but I'm not sure how much they could tell you. Check that the loft space has been double rolled. You should have the Rockwall/fluffy stuff between the joists as well as it rolled over the top again. That's what we would do but I'm not sure if that's a reg or not.

The laminate floor won't help with insulation but like you say, there isn't alot you can do about that. Ideally you would have underfloor heating but I know that can be pricey.

Try shutting off the extension from the rest of the house overnight and check back in the morning to see if you see the same temp drop. As others have said, it could be the rest of the house drawing the best out but I suspect that you would have already worked that out from previous experience of living there.
 
Soldato
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It is possible that parts of still drying out, and as such isn't set, and will improve over time.
Once everything 'warms'.
That won't make a difference due to the materials that insulation is made out of. It takes 2 years for a new build to "dry out" fully for example
 
Caporegime
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What temperature it is outside will also have a huge effect.

As in if it's 15c outside or if it's -2c outside the temperature will drop a lot more if it's colder.

My home is quite well insulated it took 7 hours to get from 10c to 17c with heating on for the full 7 hours. It is however minus temperatures here with snow and ice on the roads. It's dropped 4 degrees now in the 3 hours the heating has been off.
 
Soldato
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What temperature it is outside will also have a huge effect.

As in if it's 15c outside or if it's -2c outside the temperature will drop a lot more if it's colder.

My home is quite well insulated it took 7 hours to get from 10c to 17c with heating on for the full 7 hours. It is however minus temperatures here with snow and ice on the roads. It's dropped 4 degrees now in the 3 hours the heating has been off.
See I'm looking at the heat loss when it's ~5 degrees outside so quite a large delta. Shutting the doors not made much difference tbh. I'm not sure how your house can be well insulated if it drops to 10 degrees, ours never drops below 16 without the heating on.
 
Associate
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984
Roof would be the first thing I would check (the space above the flat ceiling) to ensure there is adequate insulation and laid properly.

We are thinking of doing an extension, hope you don't mind me asking: whereabouts are you and how much did it cost?
 
Caporegime
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See I'm looking at the heat loss when it's ~5 degrees outside so quite a large delta. Shutting the doors not made much difference tbh. I'm not sure how your house can be well insulated if it drops to 10 degrees, ours never drops below 16 without the heating on.

I've not been staying there.

So the heating has been left on 9c to stop pipes from freezing and therefore it's been hovering around 9-10.

If I'm home the heating will never drop below 16-18c because that's what a thermostat does. Keeps your home at the temperature you deem comfortable 24/7.

My home was built around 1996-1999.o it's built to quite high standards in terms of insulation. It's detached so will lose heat from every possible angle.

It's minus 3 outside. So that's why it's so low and drops so fast.

That's why it took 7 hours to get from 10 to 17.

If I didn't leave the safety temp at 9c my house would eventually drop to minus 3 also.
 
Soldato
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4 Feb 2018
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7,858
I realise this is a bit of a finger in the wind type question, but here goes. We have had a single storey extension finished recently ~2 to 3 months ago. I notice that it's losing around 5-6 degrees overnight. Is this normal? The heating is a 1kw rad in each room with 1 being 2.5m X 3.5m and the other 2m X 2.5m. the bigger room does have a window in that's about 1.8m wide, and both are essentially 2 outside walls. It's an apex roof rather than a flat roof. There is insulation in there, but not as much as I would have expected, think about 6-10 inches or so (I remember it being the thickness of the joists and they were about that). The loss is from when the heating clicks off at 10pm and it clicks on at 5 am. The drop is from 20ish to 14ish.
You might not care but do you realise you have left your address in the plan?
 
Soldato
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You might not care but do you realise you have left your address in the plan?
It's from the planning website anyway. As for the above poster we paid about 22.5k in total. That was for undecorated and unpainted. We must have spent close to a grand on decorating it. Poster directly above, I didn't realise you weren't living there, I thought you were just a miser with regards to heating:p. As you can see from the plan ours is a 3 bed detached, but also it was built mid 90s. I did look at underfloor heating but I thought it would cost too much Vs a few hundred quid on electric rads (I'm assuming running costs of electric underfloor heating is quite highl.
 
Associate
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Been skimming this as trying to figure out what insulation you have :
In roof - 100mm foil backed
In floor- some roll out stuff
In walls - cavity insulated
That right?

I had to fix our extension and put 150mm of foil backed in floor and ceiling and cavity wall insulated. It made the room usable at this time of year.
We also had huge holes hidden behind the skirting for the external vents to circulate air under the floor but they were way too big.
 
Soldato
Joined
27 Mar 2013
Posts
7,116
Been skimming this as trying to figure out what insulation you have :
In roof - 100mm foil backed
In floor- some roll out stuff
In walls - cavity insulated
That right?

I had to fix our extension and put 150mm of foil backed in floor and ceiling and cavity wall insulated. It made the room usable at this time of year.
We also had huge holes hidden behind the skirting for the external vents to circulate air under the floor but they were way too big.
Sorry the roof is the rolled out stuff. Might be the same under the floor not sure.
 
Soldato
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27 Mar 2013
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7,116
So because i'm sad i've logged it. Bear in mind that the thermostat is set to 20 but isnt actually in the same room as the measurements. Also the utility and study are electric radiators with their own thermostat sensor. It's looking like the utility is the problem, the entrance way doesnt have a radiator in but is covered on both sides. I'm wondering if the wall between the utility and the garage is not insulated?





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