Loft conversions that get too hot

[DIYedboy]

This is purely a general question, it seems all loft conversions get too hot in the summer......has this problem been overcome yet? (forgetting using aircon or mega ventilation)

 

[big-all]

hot lofts are caused by poor insulation
so done to building regs heat transfer will be minimum

 

[cjard]

major source of heat in a LC is the sun beating down on a dark roof.. as far as heating goes, that can be worth around 1kw per square metre, so if your roof is a modest 5m x 5m, it could be like sitting in the room with 25kw electric fire blazing away in the corner..

Aaand, like your thermos, that contains a boiling liquid but feels cold to the touch.. that's the power of insulation!

Works the other way too, in winter. Nothing wrong with a bit of ventilation either

 

[John D v2.0]

As said above would be the main thing, plus another point (not summer, actually in winter) would be if the doors are open all the way up and you have standard radiators, the heat may be collecting up there before downstairs gets warm. It's possible the same might happen in summer if the suns heating your hallway.

 

[DIYedboy]

Interesting CJ

My neighbours one was done 4 years ago (30's mid terrace) so it would be done correctly and that used to get pretty warm in the summer. Are you saying that the cure would be 300mm of celotex on the flat roof and all sides?

 

[John D v2.0]

Poor workmanship didn't stop at any particular time. Could have been done badly unless you inspected it yourself

 

[cjard]

As said above would be the main thing, plus another point (not summer, actually in winter) would be if the doors are open all the way up and you have standard radiators, the heat may be collecting up there before downstairs gets warm. It's possible the same might happen in summer if the suns heating your hallway.

You know, something I've always been amazed by in past properties, is that the downstairs rooms where the heat sources generally were, did a crap job of heating the upstairs rooms. Long I pondered how a block of cold air would happily sit on top of a block of warm, to the point where the drop could could be felt as I walked up the stairs

I do still wonder what physical properties exist to prevent the air moving in some situaitons but encouraging it in others. My latest house has a full height hall, 8 metres of wall. If I stand next to it I can feel the slight draught of convection - the place is wrapped in well detailed membrane so it' unlikely to be coming rom anywhere else. I wonder if warm air will collect upstairs in this one, unlike the others..

 

[cjard]

Interesting CJ

My neighbours one was done 4 years ago (30's mid terrace) so it would be done correctly

Of course..

and that used to get pretty warm in the summer. Are you saying that the cure would be 300mm of celotex on the flat roof and all sides?

It depends. 300mm of celotex is going to do little to negate the effect of the sun beating directly through 6 square metres of window and striking a black wall for 12 hours

 

[John D v2.0]

Cjard I wonder that too about the downstairs heating Upstairs. Our Hall radiator at the bottom of the stairs seems to heat the immediate area OK by radiation(!) But all the convected heat seems to go to the ceiling and up the stairs. If you sit on the stairs, you can feel a strong cold draught at door level.
My plan is to replace it with a wet fan convector to try to mix the air better, so hopefully the hot air won't all clump together and disappear upstairs.
I'd be interested if anyone has an answer for why it doesn't always happen.

 

[DIYedboy]

Isn't it the case that the reason there is a draft in the hall is because warm air rises, but as the air cools, it becomes heavier and drops down the hallway which is why people shouldn't open the lounge into the hall as they'll be suffering the downdraft

 

[cjard]

Conceptually, and incidentally this is why classically rads are put under windows.. the window is a source of cool and air convection downwards. The rad is a source of heat, convecting air upwards. The two meet and mix, and should cause a funnelling out into the room. If your rad and window were on opposite sides of the room, one heats, the other cools, and it sets up a cycle that realises a circular draft, very uncomfortable for room occupants

I know he theory, I'm just curious how some properties I've had don't seem to follow it in practice.. my brothers place has an aga and a coal fire in an open plan living space on the ground floor, and an open zigzag stair in one corner right the way to the top floor on the third storey. With the door open to the top bedroom, and aga and coal fire blazing away, the top bedroom will be like an ice box without the rad on.. the heat downstairs can be sweltering but it never makes it upstairs

Now, air is a poor heat transfer mechanism so it's reasonable not to be able to expect to heat a house via air transfer unless you have a passivhaus, but my surprise is how litttle of the warm air makes its way upstairs under its own buoyancy, convection etc. Maybe the zigging stair is enough to arrest it..

BY contrast my house has no staircase fitted at the moment so the hall wall is just a massive vertical surface 8 metres high. There's definitely a slow draft, or was the other day when the plasterer had had the windows open upstairs cooling it considerably.
the heating system in my place is the opposite of my brother's; underfloor heating at max 22 degrees, an air source heat pump, and the entire place sealed against drafts meticulously. Today the thermostat on the ashp control unit read 15 degrees and both me and the plasterer would have sworn blind the house temp was in the twenties, apart from in the hall. It's a curious effect when there is no air movement

 

[DIYedboy]

If your brother's house has a cold loft n no loft insulation that would probably keep the top storey cold. If he's detached with solid walls each storey will suck out the heat