Warm roof construction

M

marsaday

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I would like to reroof this house in the photo. it has one pitch only.

i dont have to improve the insulation for regs or anything like that, but if i do reroof, i would like to go for a warm roof construction.

is the following the correct way of doing the roof:

i will use 50mm celotex between the rafters and 50mm over them (remember i dont need to meet regs).

The tile battens will then be screwed on top of the celotex. The tiles will be nailed to the battons.

i dont need a breather membrane or any venting.

Can anyone see any faults in my thinking. i am just researching this type of roofing system you see.
 
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The tile battens will then be screwed on top of the celotex........
Can anyone see any faults in my thinking.

Yes i can.

You need to fix a counter batten through the celotex (to the rafter) then fix your tile battens to the counter batten.
 
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Hi

Why don't you do the opposite and fix the insulation from in the loft - 50mm between rafters, 50mm across the rafters and save yourself all the extra work? This will also give you around 25-50mm void between the insulation and the roof finish.

Use a PIR which has a lot higher vapour resistance than the other forms of insulation as this will mean you won't need a vapour barrier! You will also maintain an air gap between the insulation and the roof covering which will allow the void to breathe - as you are going to get condensation form from time to time on the underside of the slate. Use an alternative insulation and you will find performance of the insulation suffer due to interstitial condensation.

Regards
 
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M

marsaday

The tile battens will then be screwed on top of the celotex........
Can anyone see any faults in my thinking.

Yes i can.

You need to fix a counter batten through the celotex (to the rafter) then fix your tile battens to the counter batten.


ok so these first fix battens will run the length of the rafters then (vertically running)? As the next set of battens will go across the roof horizontally.

Why do i need 2 sets of battens?
 
M

marsaday

Hi

Why don't you do the opposite and fix the insulation from in the loft - 50mm between rafters, 50mm across the rafters and save yourself all the extra work? This will also give you around 25-50mm void between the insulation and the roof finish.

Use a PIR which has a lot higher vapour resistance than the other forms of insulation as this will mean you won't need a vapour barrier! You will also maintain an air gap between the insulation and the roof covering which will allow the void to breathe - as you are going to get condensation form from time to time on the underside of the slate. Use an alternative insulation and you will find performance of the insulation suffer due to interstitial condensation.

Regards


i need to insulate the roof, but it also needs a re-roof. So i can kill two birds with one stone by doing all the work from the top. i do not need to remove the plaster that way.
 
M

marsaday

Another question !

I will be raising the roof height by 75mm (50mm of insulation and 25mm extra batten). This will mean at the sides where the roof meets the walls there will be a gap of 75mm as opposed to 25mm. Previously this gap was filled with mortar. What should i use to fill the bigger gap ? Mortar again?
 
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Insulation on rafters.

Counter-batten.

Felt or roofing membrane.

Roofing battens or lathes.

Tiles.

You will need to form a lead flashing on the upstand where the roofs differ in height.
 
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Increasing the height is a lot more hassle than just adding 50mm or so beneath the rafters. You will have to get all the flashings redone higher up and possibly raise the gutters too. Using a breathable membrane would be cheaper than all that malarky.
 
M

marsaday

yep i think i will insulate from underneath and see if i can patch repair bits of the roof.
 
M

marsaday

ha ha. Well what i have read says insulate from underneath. so that is what i will go with.








Then again.......
 
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No outside has got to be better... don't listen to them lot, they got it all wrong!

Nah, inside is the sensible choice. The roof covering doesn't look bad enough to replace, as you say, patch up the dodgy and insulate from below.
50 between and 50 below, poly vapour barrier, PB over. (You know all this though from previous questions) If you ever get the roof redone in the future then you can drop some more inso in from the top and breather over the top.

...so, as I was just saying, strip it all off, knock the house down rebuild from scratch in MDF, flat roof etc etc
 
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Hi!

If your going to insulate from inside, then never think of filling the air gap between the slates and the insulation - If you decide to fill the air gap, whatever else happens you are going to get condensation between the underside of the slates (or sarking felt) and the top of the insulation.
If the roof can't breathe then the rafters are going to become saturated from time to time and without going into too much detail you could find yourself having to replace the rafters because of timber decay from wet/dry rot!


Regards
 

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