My 1905 year old slate roof needs some work doing.. quite a lot of work. More slates are held on with bits of wire than are actually nailed on! Ridiculously complex roof with plenty of valleys and ridges (though on the image- only the front half of the house is mine!)

The top floor of the house protrudes into the roof by 1.2m with sloped surfaces. These are insulated internally with 50mm of PIR. There is also 250mm of mineral insulation in the loft on the flat portions of ceiling. There are cold bridges where the wooden joists block the mineral insulation but aren't sloped to be covered by the PIR. I should have put PIR on the flat ceilings too.. but hindsight...

So given I'm going to get the roof redone anyway- what can/should I do to further insulation? Currently it's just slate- no felt. Joists seem sound, cross battens (I'm not very good on roof terminology, sorry!) really all want replacing I'd say. Lead valleys seem watertight, some of the chimney flashing needs redoing (there's 3 chimneys). Most roofers will strip slate off, replace wood, put felt and slates back on. But then I might be missing a chance to insulate further and I'm of the opinion that you probably can't have too much insulation.

Redo all leadwork

Re use the slates they look like good ones ally or copper nails

New battens,

Posted By: Pile-o-StoneWhen we stripped our roof, we fitted TLX Gold multifoil insulation on top of the rafters (this is a breather membrane and mutifoil in one product, with a 75mm air gap and 25mm celotex between rafters and 100mm celotex beneath the rafters.

Woohoo! Multifoil is still alive! How I miss that thread ;)

Paul in Montreal.

I think I'm asking the wrong tradesmen- they've all looked at me like I've got a second head when I ask about insulation. They're more than happy to just 'redo the roof' as in replace battens/leadwork/etc but don't want anything more complicated.

Something along the lines of TLX gold, some PIR between rafters (I've no idea what size the rafters are actually, will have to go up and measure) and if necessary some underneath (there's already 50mm on the room sloped surfaces) would be ideal (can't change the roofline- conservation area!).

Oh, and to find a roofer willing to fit this stuff properly! I draw the line at dancing around on the roof for DIY.

I'm in Derbyshire, if anyone has any suggestions :)

Currently the loft is cold- in that the insulation is in the flat ceiling. However the upper floor of the house extends up into the roofspace- these sloped bits of roof in the upstairs rooms are internally insulated (with 50mm PIR). And there are cold bridges where timber exists between the two types of insulation.

I can have external-access to the roof, and internal access to the loft- however the actual loft is only 1.4m tall so you can't really work in there. Thinking about it I can't see how I could attach sheets of PIR in there- you wouldn't be able to maneuver anything! And it is a really complex shape.

I was hoping I could increase the insulation of where the rooms protrude into the roofspace from the external of the roof.

I'm in a conservation area so I can't change the roofline- but may get away with less insulation than the regs mention if it is impossible to fit it.

The council outsource all building regs work to an external company, who won't talk to me until I give them money. But given they haven't said they can help with what I am asking, I don't feel inclined to give them money quite yet.

Posted By: djh

Posted By: CharliCurrently the loft is cold

And presumably ventilated?

By the massive gaps between the slates, yes!

Yep!

Charli, are you only prepared to do insulation on the 'cold side' - in the voids where it won't have to disturb ceilings etc.? Are you going for 'best you can', or have you got an overall Plan? How about drawing it out, estimating U values (or calculating - it's easy) for each area, and looking for 'weak spots'? Don't forget to calculate (and discount for) the timber fraction (the amount of the 'insulation' that's wood).

I would not use multifoil, by choice. I don't claim it's the makers' fault, but I have seen it used wrongly, and where I have seen it used in conjunction with PIR the much-discussed space-gains (or reductions in losses) have seemed minimal. If I were using PIR ( or Pu) anyway, I'd probably just use more.

Watch out for potential thermal by-pass between layers of insulation where the ventilation enters at the eaves. Consider a 'deflector' of breathable membrane.

Posted By: tonyReroofing triggers part L1b of the building regulations and though never enforced the require the insulation to be upgraded as part of the works.

I'm in a conservation area, so if I can't physically fit enough insulation in I can apply to not have to meet the building regs. No idea if the council would accept this or not.

Posted By: Nick Parsons
Charli, are you only prepared to do insulation on the 'cold side' - in the voids where it won't have to disturb ceilings etc.? Are you going for 'best you can', or have you got an overall Plan? How about drawing it out, estimating U values (or calculating - it's easy) for each area, and looking for 'weak spots'? Don't forget to calculate (and discount for) the timber fraction (the amount of the 'insulation' that's wood).

Only prepared to do the cold side at this point- the inside was 'done' 6ish years ago. I have no plan, other than I wanted some ideas to propose to roofers to make sure 'something' was done. So far they seem happy to do nothing- which I don't want!

Posted By: WillInAberdeenWe got more interest from joiners than from roofers about insulation.

For the small triangle attic area, just add lots more mineral wool on top of the ceiling, joiner does this later, or DIY. Maybe need to add ventilation slates to compensate for loss of gaps between slates. (Edit: this would often be done with vents in the soffits, but you hardly have any soffit between the windows! Do you need any work on the timber, repairs to fascias bargeboards etc? Joiner does this while scaffolding is up. Take opportunity to paint?)

I'll try asking some other trades- good idea.
There's mountains of mineral wool on the horizontal ceiling already (over 300mm)- but if I PIR the sloped ceilings then it might make sense to do the whole roof up to the peak (or it might not, I don't know!). There's big bits of timber at this junction that currently are a cold bridge (not at the eaves, but where the flat ceiling becomes a sloped ceiling- the mineral wool has to be clear of the wood for ventilation and the PIR doesn't start until under the timber).

If there's a scaffold up I could potentially do the insulation myself. I wouldn't mind that.

Have finally been up in the loft! My rafters are 70mm (and there's lots of them) which is useful in that most u-value calculators won't accept rafter sizes that small.The batons are then 20mm, which doesn't give me very much room for fitting any insulation between rafters.

If I need 50mm gap between slates/membrane and insulation- then I'm assuming this includes the depth of the baton? So that gives me 40mm of insulation. There's already 50mm fitted internally inside the rooms, gives me a u value of 0.21 (and I'm just ignoring the timber portion here but its significant).

Really hard to maneuver up there!

Looks very like one I have just been working on! In my case I had the ceiling down, ran quilt over the joists and tightly fitted PIR between.