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Mounting on top of insulation

Discuss Mounting on top of insulation in the Solar PV Forum area at ElectriciansForums.net

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yellowvanman

Electrician's Arms
Just did a survey and customer intents to re-tile roof but wants to put 3-4" of rigid insulation between the rafters and battens. How do you mount your brackets on to this?
 
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GaryM

Is that usual? I've only ever seen kingspan, celotex etc cut and fitted between rafters, not on top of them.
 

yellowvanman

Electrician's Arms
He was an architect, so I guess he knows what he's doing.

I've seen this once before but the insulation was sandwiched between some sort of rigid sheet - can't remember what it was but fairly sure it wasn't wood.
 

whinmoor

Electrician's Arms
Have you considered integrated panels or solar tiles? I guess an architect's into his technical drawings and appearance of buildings so he might prefer the look. It would be an interesting project for the installation team as well working with different components. Not sure about the cost element but if he's planning to re-roof anyway it might save on labour. materials and weight.
 

moggy1968

Electrician's Arms
about half of what an Architect designs would fall down if it was ever built!
You know what RIBA stands for don't you, Remember I'm the Bloody Architect!!
I suspect what his is intending to do wouldn't pass building regs. The battens are only there to stop the tiles sliding off. the main structural support is from the rafters. If he puts a non ridgid insulating layer between the rafters and battens then over time his roof will sag under the weight and go all wavey!! The strongest part of his roof will be your rails!!
Are you sure he isn't intending to insulate between the rafters themselves, not between the rafters and battens?
 

yellowvanman

Electrician's Arms
Are you sure he isn't intending to insulate between the rafters themselves, not between the rafters and battens?
No. When he said it I thought it strange! Will have to confirm and if I interpreted correctly will have to tell him to re-think!
 
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GaryM

I have also seen kingspan and celotex fixed on the underside of rafters and then plasterboard for loft conversions and open ceilings.
 

moggy1968

Electrician's Arms
yes, thats common practice, but thats not the same as insulation between the rafters and the battens!
If this is what he intends doing I think he has been sniffing something!!
 
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GaryM

I know. Just wondering if there's a mixup on which side of the rafter the insulation will be fixed.
 

solarsavings

Electrician's Arms
If he adds insulation over the rafters (and usually between the rafters too) the roof will be counter battened so fix through the counter batten with a fixing like fastenmaster.
 

screwdriver

Electrician's Arms
The design you are referring to is called a warm roof, it is becoming more common in new builds as it is much easier to ensure consistent insulation detailing. (also a damn site easier to fit down lights in between rafters when there is no insulation!)

As Solarsavings says you can fix through the counter batten with a really long fixing to pick up the joist behind, or if you have sufficient batten size and a structural engineers approval you may be able to just fix to the counter batten.
 

Graeme Harrold

Electrician's Arms
Saw this being done to buildings outside the Iona ferry point, King span fitted over wood cladding, then battened, then slated re,fitted. Could be a tricky one to fix to due to the standoff distance between solid components, and may need to fix noggins and through bolt....speak to the architect!!
 

screwdriver

Electrician's Arms
The counterbattens run down directly over the rafters and are in effect sandwiching the insulation board and so once you have pre drilled and screwed all the way through the counter battens into the rafter you then have virtually no compression of the insulation. You have to remember that counterbattens are already going to be taking the load of the tiles and so are able to take a large load without the insulation compressing. This is fresh in my mind as the guys on site have got one to do tomorrow, out of all our jobs I reckon we have only done 2% warm roof installs so it either shows how few newbuilds we do or that the customers that have PV live in older houses!
 
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