Keeping the loft space cool?  


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Hi all, I had cause to enter our loft today, which is well insulated at rafter level but due to the hot weather and blazing sun, the heat in the space was truly unbeareable.

Is there a way to insulate under the decra tiles themselves in an attempt to reduce this heat?

 
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Hi DrJohn,

If the loft was well insulated at rafter level it shouldn't be too hot in the loft. Did you mean it is insulated at the joists? I'd be surprised if it were insulated at the rafters as I'd imagine a BISF loft would be too small to justify a loft conversion.

If it's insulated at the joists rather than the rafters, the upstairs ceiling is your heat loss perimeter and the rest of the loft above this is effectively 'outdoors'. If this is the case it's probably best to just accept the loft will be cold in winter and hot in summer.

Did I understand your question right?

 
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Hello Owen, thank you for your reply.

My sincere apologies as I must confess, I do not know my rafters from my joists. You are correct though, as I refer to the joists onto which my ceiling boards are affixed from the first floor bedroom.

I understand from gleaning some of the excellent information available here that the cavity of the house is free venting and as such, air can circulate freely through the cavity and into the loft space.

In the winter time, I notice condensation forming on the underside of the steel roofing system membrane. I presume this is due, in part to the fact that the war air from the house, escapes into the cavity and due to EWI, it retains both warmth and moisture as it rises into the loft, thus condensing on the cold underside of the roof tiles.

Having recently entered the loft space during our current heatwave, I noticed nothing but extreme heat in the loft and the underside of the steel roofing sheets were terribly hot to the touch, despite the rubber type membrane between the steel tiles and my hand.

My thoughts turned toward the possibility of bonding eps polystyrene panels or reflective bubble insulation directly to the underside of the roofing material, in the hope that it would help keep the heat out (and prevent it from entering the upper floor bedrooms) whilst also preventing condensation from forming in the winter months.

How effective this may be, I do not yet know but I do feel that it should be addressed in my daughters home.

I would  appreciate your thoughts on this.

With thanks

John

Hi John,

No need to apologise. What you describe is the norm for most houses, unless they have a room in the roof.

I'd say a small amount of condensation on the underside of the steel roof would be acceptable in winter. Too much would suggest the ventilation under the eaves has been blocked and should be addressed - especially in a steel structure. The idea isn't for the air to just gather in the loft but to vent out under the eaves.

Likewise, I'd expect the steel roof to be hot to the touch in summer. Just like your car roof would be. The insulation at your joists should be stopping the upper floor from being heated in summer and cooled in winter. If in doubt, add more insulation at the joists. 300mm should be plenty but more won't hurt. The loft is effectively outside; it's heat passing through the upper floor ceiling level that you want to minimise.

If the comfort level in the loft space is still important to you after assuring yourself the living area is well insulated, yes you can insulate at rafter level. This would have negligible to nill impact on the living areas of the house but would make it more comfortable on the occasions you go into the loft.

I think you are on the right track with the EPS panels but ideally would suggest you don't attach it directly to the roofing sheets. Not from an efficiency point of view but from thinking about future roof work. Insulation boards bonded to the back of the roofing sheets could make a real mess of any repair and replacement jobs. Much better to mount them on a mounting system ideally. And to do the job properly don't forget the gable end, which is also a heat loss surface. For me I'd consider it a lot of effort and expense for minimal gains but I haven't experienced your loft on a hot day!

Hope this helps.

Owen

  
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