Ventilating loft to lower temperature upstairs.

justwantedtosay

Hi

Has anyone any experience of cooling their loft to cool their bedrooms?

Mine has slatted soffits for ventilation but nowhere for the air to escape so it gets extremely hot - there's no air movement at all unless it's windy - and despite plenty of fibre insulation [I put another 6" on top of what the builders gave me] this heat gets through to the rooms upstairs. I was wondering whether an in-line fan and ducting to pump relatively cool air through the soffit on north side of the house up to the ridge which would presumably then push the hotter air out of the rest of the vented soffit would help, though perhaps it would just replace very hot air with less hot air. An alternative might be vented ridge tiles but that's not something I could do myself and though they'd have no running costs they'd be more passive than a fan and perhaps less effective? Maybe neither would make much difference? People suggest that insulation under the tiles - not sprayed foam, I'm not considering that! - is likely to cause damp problems and is pricey and would be difficult to fit in my space anyway. Perhaps there's no answer but to grin and bear it until autumn. The loft is just a loft, not a living space.

Cheers.

grumpy_codger

justwantedtosay said:

...despite plenty of fibre insulation [I put another 6" on top of what the builders gave me] this heat gets through to the rooms upstairs. 

How do you know that it's hot upstairs because of this? In my house  temperature upstairs is 3-4 degrees higher throughout the year including winter when the loft is much colder. And this isn't because I heat it more, quite the opposite.

I was wondering whether an in-line fan and ducting to pump relatively cool air through the soffit on north side of the house up to the ridge which would presumably then push the hotter air out of the rest of the vented soffit would help, though perhaps it would just replace very hot air with less hot air. An alternative might be vented ridge tiles but that's not something I could do myself and though they'd have no running costs they'd be more passive than a fan and perhaps less effective? Maybe neither would make much difference? People suggest that insulation under the tiles - not sprayed foam, I'm not considering that! - is likely to cause damp problems and is pricey and would be difficult to fit in my space anyway. Perhaps there's no answer but to grin and bear it until autumn. The loft is just a loft, not a living space.

IMO, pumping out is better.
Insulation between rafters works well. I have a lot of polystyrene packaging between mine. BnQ sell some special polystyren boards.

justwantedtosay

grumpy_codger said:

justwantedtosay said:

...despite plenty of fibre insulation [I put another 6" on top of what the builders gave me] this heat gets through to the rooms upstairs. 

How do you know that it's hot upstairs because of this?

Because I can feel how hot the ceiling is.

WIAWSNB

Hi JWTS.

Almost certainly your bedroom ceilings are 'hot' from the heat in the bedroom - hot air rises - and not coming through from the loft.

You have done the right thing by insulating your loft well - that works both ways, in reducing heat transfer both up from the bedrooms, and cold down from the loft (it's the same thing). 

Yes, you could rip out your bedroom ceilings, and that would allow the trapped air to escape that way, but it isn't a practical solution. 

You just need to ventilate the bedrooms themselves - leave the windows open to allow a through-draft, but keep the sunny-side curtains pulled to cut down solar gain. You may find it's better to keep the bedroom doors shut, as this will only supply warm air from the rooms below, but experiment with this. For instance, if a bedroom has only a single aspect - ie window on only one wall - then it'll likely be better to leave the door open, so it gets a through-flow from other rooms. For dual aspect, try keeping the door shut, and both sets of windows as open as possible - again curtains pulled on the sunny side. 

'MyCarbon' makes fans which are whisper-quiet - as I'm sure do others - so you could always try this as a not-too-costly option. That, coupled with only a loose sheet at most. I recall a really hot summer from '96(?), where I also had a water trigger spray which I'd fire up into t'air, so it would lightly douse me and the sheet. 

justwantedtosay

WIAWSNB said:

Hi JWTS.

Almost certainly your bedroom ceilings are 'hot' from the heat in the bedroom - hot air rises - and not coming through from the loft.

That's definitely not the case.

GDB2222

I’d try an experiment with a fan or two blowing air towards the soffits. See if it helps. 

twopenny

I used to open the loft hatch which was outside the bedroom 
Hot air bellow goes up so went there.

The insulation did not cover the eaves for ventilation and so allowed a change of air.

Also open windows on either side of the house and it will draw a draught through 

WIAWSNB

justwantedtosay said:

WIAWSNB said:

Hi JWTS.

Almost certainly your bedroom ceilings are 'hot' from the heat in the bedroom - hot air rises - and not coming through from the loft.

That's definitely not the case.

Ok, fair do's. 
But, the heat from the loft will be lessened if the insulation layer is good.
Put it another way - if you remove the loft insulation, will more or less heat from your roasting loft come through your ceiling?
And in winter, will more or less 'cold' come ditto?
If your bedrooms are too hot - and many are in this unpleasant spell - then the bedrooms need addressing, not the loft :-)
Ventilation, fans, even portable air-con.

justwantedtosay

twopenny said:

I used to open the loft hatch which was outside the bedroom  

Thanks. I'm doing that, but as the air in the loft is so much hotter than the air in the bedrooms I'm not convinced the less hot air would rise into the loft. If the loft were cold, as in winter, then I've no doubt the heat would disappear through an open hatch - not so sure about the summer situation. Anyway, if the warm air did leave the living-in part of the house for the loft it would have to be replaced and that could only come from outdoors which is hotter than indoors so surely that would just make the house hotter...? I can smell hot wood when the hatch is open - it's like an oven up there!

twopenny

I shouldn't laugh but your description did make me chuckle 🙂
I know how desperate it can be. It got so hot in the loft it popped the hatch down in the middle of the night in my last place.

Won't help tonight but if there's no breeze at all I have used foil security blankets taped or clipped over the windows. They are amazing. It's degrees cooler behind. Cost about £3 for a few online.
Before that I used the car foil window shields. Not as good but better than nothing.

stuart45

Lofts do get incredibly hot in the summer, especially when not insulated at rafter level. 
Insulation at joist level will still allow a certain amount of heat through to the ceiling below. 
One point about cold in the winter. Insulation stops the majority of heat escaping, but cold isn't an energy force, so it can't come back. Cold is really just a lack of heat, so even cold air contains a certain amount of heat, which is why heat pumps can still work in the winter.