I think my outbuilding isn't insulated enough...

[Bob Harris]

my outbuilding consists of a single skin brick wall, breather membrane, batten, and Celotex PL4000 insultation board (60mm foam insulation & 12mm platerboard) The ceiling is the same Pl4000 board screwed to the underneath of tapering roof joists. Joists are hollow and vented front and rear. Sitting on top of the joists the top deck is a simple water bonded 18mm plywood covered in felt.

The room heats up nicely, but within 30minutes of tuning off the heater the room becomes cold, uncomfortably so after about an hour.

Is this normal or am I outrageously under insulated? Before the build I contacted Celotex and they informed me that the boards they recommended would provide better insulation than a standard house.

Is this true, or was i lied to?

 

[Doggit]

The question to the possible lie, would be how they define a standard house; is that one with an 11" brick wall, or a cavity wall insulation property.

I'd say that you've definitely improved on the 11" wall building, but not reached a cavity wall standard yet, but that might be a bit unreasonable to expect under the circumstances. Can you apply any insulation to the floor to improve things.

 

[endecotp]

What's the construction of the floor?
Is there good draughtproofing around the door?

You might also think about "thermal mass". If you have good insulation but low thermal mass, the room will be cheap to heat but will heat up and cool down quickly. If you have poor insulation but high thermal mass, the room will be expensive to heat but warm up and cool down slowly.

 

[Bob Harris]

What's the construction of the floor?
Is there good draughtproofing around the door?

You might also think about "thermal mass". If you have good insulation but low thermal mass, the room will be cheap to heat but will heat up and cool down quickly. If you have poor insulation but high thermal mass, the room will be expensive to heat but warm up and cool down slowly.

The floor is concrete covered with vinyl. The door is wood, but a good tight fit.
I do find the room nice and cool when entering in the summer. The room takes around 1 and a half to two hours to heat up but as i said before, cools down within an hour.

I wish i could get my hands on one of those thermal gun things to so that i could maybe see cold spots.

If wonder if i should convert the roof to a warm roof. I know that a cold roof has insulation between the joists with a minimum of 50mm air gap, but mine has insulation on the underneath of the joists. What would you call that?
When i replay my felt for that rubber stuff in the future i could then take the opportunity to have some insulation laid on the top deck and between the joists.

 

[Doggit]

As I suspected, it's the floor that's the issue. Vinyl has no insulating properties in it, so the floor is taking a lot of the heat as the room warms up, but then it's escaping out through the roof as it cools down, as the floor is then a heat sink, and will retain it. Do you have enough space to lay some UFH insulation on the floor, and then add some self leveling compound.

There are thermal imaging devices for phones now. Look for FLIR One, and Seek thermal camera.

 

[jeds]

I often specify the equivalent Kingspan board on walls for garage conversions. It doesn't quite meet u-value but it's good enough for a conversion. But it's not enough for a roof. I would have fitted 100mm between rafters and 40 or 50mm continuous layer under. As above you should also insulate the floor. Probably minimum 70mm PIR but I usually default to 100mm.

 

[Bob Harris]

As I suspected, it's the floor that's the issue. Vinyl has no insulating properties in it, so the floor is taking a lot of the heat as the room warms up, but then it's escaping out through the roof as it cools down, as the floor is then a heat sink, and will retain it. Do you have enough space to lay some UFH insulation on the floor, and then add some self leveling compound.

There are thermal imaging devices for phones now. Look for FLIR One, and Seek thermal camera.

I have the room to insulate the floor at the cieling is quite high, but it would be quite a hassle because the skirting board has been gluded to the walls.

 

[Bob Harris]

I often specify the equivalent Kingspan board on walls for garage conversions. It doesn't quite meet u-value but it's good enough for a conversion. But it's not enough for a roof. I would have fitted 100mm between rafters and 40 or 50mm continuous layer under. As above you should also insulate the floor. Probably minimum 70mm PIR but I usually default to 100mm.

Could i insulate between the joist and on top of the top deck when i replace the roof felt? How much can i expect to pay to insulate a 12" square roof?

 

[Doggit]

I have the room to insulate the floor at the cieling is quite high, but it would be quite a hassle because the skirting board has been gluded to the walls

I'm not sure what you're using the garage for now, but as you've currently got vinyl down, then this will go back down up against the skirting board, otherwise, use quadrant to cover up any problems. Building regs on a loft conversion would normally ask for 100mm between the rafters, and 35mm+plasterboard under the joists, so you're definitely underspeced.

How much can i expect to pay to insulate a 12" square roof?

You just need to get quotes I'm afraid. Work out the material costs, ask the builders how long it will take, and that'll give you the material costs, and the man days, and you can then do a few quick and dirty calculations to see how fair the quotes are. My partners just been quoted £1200 labour to lay 20 sqm of 600x600 tiles. The guys said it'd take them 2 days, but I know 2 men can do that in a day, and then a few hours the next day to grout. So that means £1200 for effectively less than 3 days work, or £450 per man day. She declined the offer.

On the other hand, which will cost less, taking down the existing ceiling, and putting 140mm of pir between the joist, which you can do yourself, then just plasterboard it, or take the roof off, insulate, and relay the roof. Check ebay for seconds and co for cheap celotex