Lining and insulating loft before/after getting solar panels installed

[Derek M]

My Dad's getting free solar panels installed, so the installers have got to setup the scaffolding for that. They've said that if there's a few tiles that need replacing they'll do that whilst they're up there.

He also wants to fit some internal lining in the loft to stop dirt getting in and also to stop it getting so hot in summer and cold in winter, so I was wondering whether it would be sensible to have someone ready to do that whilst the scaffolding is in place in case they need external access, or is there no chance of that being necessary and we can just wait and get it done any time, or just do it ourselves?

I've attached some photos showing the roof at the back where the solar panels will be going and inside the loft. There's some sort of wooden cladding on the inside of the roof, so the tiles aren't visible. Would foil lining be OK, or should we use a breathable membrane? Do you just staple it to the inside edges of the rafters?

As well as lining it, we'll want to add some insulation and I was thinking that a sheep's wool product like this https://thermafleece.com/product/thermafleece-cosywool-sheep-s-wool-flexible-slab or this https://www.celticsustainables.co.uk/thermafleece-cosywool-sheeps-wool-insulation/ would be best, as it delays the heat transfer better than rockwool, so in the summer it will stop the heat from outside making the loft unbearably hot (which then transfer down into the bedrooms) and in the winter it will stop the heat being lost through the roof, and it also absorbs and releases excess moisture which might protect the wood better. Can we just wedge it between the rafters, or do we need to staple some wire netting to them to hold it loosely in place without it being tight against the rafters and the lining?

 

[Deleted member 174758]

There's some sort of wooden cladding on the inside of the roof, so the tiles aren't visible. Would foil lining be OK, or should we use a breathable membrane? Do you just staple it to the inside edges of the rafters?

Those look like sarking boards - common in Scotland and some parts of northern England because they help make the roof more weather tight and warmer. The felt or membrane is nailed onto the outside of those then the battens (slate/tile laths), then the tiles.

I'd probably insulate between the battens with a 50mm air gap between the top of the insulation and the sarking boards. Staple chicken wire, or even just strings across the joists to keep it in place.

Any membrane goes beneath this, but if you seal the inside of the roof with a foil lining will there be sufficient ventilation to allow any moisture build up to escape?

BTW it is highly unlikely that the installers will need access to the outside of the building

 

[Derek M]

Thanks. We live in Surrey/Greater London so I guess it's not so common down here. If there was felt/membrane on the other side though, wouldn't that stop the dirt getting in already?

Yeah, I'm concerned about whether it's safe to use a foil lining or whether we need to use a breathable membrane instead, or just no lining and rely on the sheep's wool or rockwool insulation to act as a barrier to stop dirt getting in, but I'm not sure that would work as the insulation is breathable. I don't know if a breathable membrane behind breathable insulation would be any better though. What do installers do to allow sufficient ventilation with loft conversions, where they insulate between the rafters and then cover it all with plasterboard?

If we want to get some quotes for fitting the lining and/or insulation, would we need a roofer or is there another type of tradesman who could do it just as well for less than a roofer would charge?

 

[Deleted member 174758]

Thanks. We live in Surrey/Greater London so I guess it's not so common down here. If there was felt/membrane on the other side though, wouldn't that stop the dirt getting in already?

If the house was built in the coal fired period (prior to the 1970s) there will be a lot of soot and general grubiness in the attic already. Add to that lime mortar and/or lime plaster and decades of human habitation and there will be all sorts in your attic already

What do installers do to allow sufficient ventilation with loft conversions, where they insulate between the rafters and then cover it all with plasterboard?

On a previous house we had to have vent tiles installed. On some of the builds I've worked on they just went for air space, mineral wool, plasterboard then plaster skim

If we want to get some quotes for fitting the lining and/or insulation, would we need a roofer or is there another type of tradesman who could do it just as well for less than a roofer would charge?

There are some specialist insulation firms out there

 

[Derek M]

If the house was built in the coal fired period (prior to the 1970s) there will be a lot of soot and general grubiness in the attic already. Add to that lime mortar and/or lime plaster and decades of human habitation and there will be all sorts in your attic already

Yeah I guess, but a lot of that old dirt should be under the insulation and floorboards we've fitted, so the fact that stuff is still getting covered in dirt suggests that new dirt is coming in from outside.

I don't want to waste money fitting a lining if there's already one under the sarking, but I need to be sure because if there isn't one there already we should probably fit one before fitting the insulation. I guess if the solar panel installers need to replace any tiles, they'll be able to see if there's a lining there already.

On a previous house we had to have vent tiles installed. On some of the builds I've worked on they just went for air space, mineral wool, plasterboard then plaster skim

I guess it's less likely to be a problem if we're not planning to cover the insulation with plasterboard, as long as we leave an air gap between the insulation and the sarking and use a breathable membrane rather than foil for any lining.

There are some specialist insulation firms out there

They'd probably charge even more than a roofer wouldn't they? That seems to be what happens with firms that market themselves as "specialist". I was thinking more of a general handyman who's happy sticking a ladder up in the loft to fit the insulation/lining. As long as we use a breathable membrane (or no lining), rather than foil, and make sure they leave an air gap, we wouldn't really need anyone with "specialist" expertise would we?

If we were keen to use foil for some reason, then I could see that we'd need a specialist to advise whether that's safe but if we just rule that out I can't think what else we'd need specialist advice about.

 

[Deleted member 174758]

They'd probably charge even more than a roofer wouldn't they? That seems to be what happens with firms that market themselves as "specialist". I was thinking more of a general handyman who's happy sticking a ladder up in the loft to fit the insulation/lining. As long as we use a breathable membrane (or no lining), rather than foil, and make sure they leave an air gap, we wouldn't really need anyone with "specialist" expertise would we?

It depends on how efficient you want the insulation to be. We stopped using labourers or handymen to install insulation so quite a few years back (I work in construction for a joinery contractor, but we often get the job of installing insulation) - they invariably miss bits, undercut materials (so they are too small and tend to fall out) and where air gaps are needed they don't seem to understand why and often stuff the insulation in hard against the undersides of the roofboards because they simply don't know any better. Both can be, let's say, a bit variable - thinking of one in particular who posts on here...

BTW, on the insulating material front an equivalent thickness of PIR insulation, especially if installed tightly, or using a sealing strip around the outside such as Gapotape is considerably more efficient than mineral wool or sheeps wool. On the other hand, mineral wool and sheeps wool are far better noise insulators. Just so you know

 

[Derek M]

Hmm, I'll avoid using labourers or handymen to install the insulation then.

Can PIR insulation just be wedged in between the timbers, without needing any netting or rope to secure it? Gapotape sounds worth using to seal it but I wouldn't want to rely on that to hold the PIR in place.

We're not really concerned with noise insulation as we're not converting the loft into a living space, although I suppose it might be worth using sheep's wool now anyway, so that it can be reused if the loft is ever converted.

The main reasons I was thinking of using sheeps wool is because it regulates humidity by absorbing excess water vapour as the relative humidity in a room rises and then releasing it as it falls; it absorbs water without the wool feeling damp, which protects the surrounding timbers from moisture and prevents mould; and it has a higher R-value than fibreglass, which should hopefully prevent the loft getting too hot in the summer and stop it losing too much heat in the winter.

It sounds like PIR has a higher R-value than sheeps wool but how does it compare in terms of regulating humidity whilst protecting the timbers?

 

[Deleted member 174758]

Can PIR insulation just be wedged in between the timbers, without needing any netting or rope to secure it?

Yes, but the PIR needs to be cut tight to the gaps. For a DIY installation you could also use expanding PU foam to "glue" the PIR in place. Gapotape will hold PIR in place beneath ceilings, etc and TBH it is more or less mandated on new build work now.

It sounds like PIR has a higher R-value than sheeps wool but how does it compare in terms of regulating humidity whilst protecting the timbers?

AFAIK PIR requires ventilation because it doesn't absorb or release moisture

 

[robinbanks]

I was once a big fan of PIR, but having seen it shrink, these days I'd probably full fill the cavity between the rafters with wool, go over the rafters with foil faced PIR, tape the joints and board over. Moisture would be dealt with via an MVHR

If it wasn't being turned into a habitable room I wouldn't do any of it, just staple breathable felt up to catch dirt if that was a concern

 

[foxhole]

Why waste money making an empty loft comfortable? Better adding insulation to keep house warm not loft space .

 

[robinbanks]

Perhaps OP wants to store something that needs a more consistent environment..

 

[Derek M]

Why waste money making an empty loft comfortable? Better adding insulation to keep house warm not loft space .

It's partly to keep the dust out so we can store stuff up there without it getting filthy, and partly to stop the space getting boiling hot in the summer and freezing cold in the winter, which prevents us accessing the space but also the heat/cold transfers to the rooms below so insulating the loft will help keep those rooms at a more comfortable temperature in the summer and reduce the heating bills in the winter.

 

[foxhole]

It's partly to keep the dust out so we can store stuff up there without it getting filthy, and partly to stop the space getting boiling hot in the summer and freezing cold in the winter, which prevents us accessing the space but also the heat/cold transfers to the rooms below so insulating the loft will help keep those rooms at a more comfortable temperature in the summer and reduce the heating bills in the winter.

No, it won’t.

 

[robinbanks]

Given the stated complaints, for the dust n dirt issue I would buy a roll of roofing felt and staple it to the underside of the rafters (Not pulled tight, then wedge the felt open at the overlaps with short sticks. Work top down) and insulate the floor well

This will stop stuff getting quite so covered in crap, leave gaps in the felt for ventilation, and keep the insulation close to the warm envelope of the house that is actively used.

You sure could go to the effort and expense of insulating the loft and dealing with accumulating moisture in a way that means the insulation remains effective but if you're not going to convert it to a habitable room it's money wasted imo

 

[Derek M]

Given the stated complaints, for the dust n dirt issue I would buy a roll of roofing felt and staple it to the underside of the rafters (Not pulled tight, then wedge the felt open at the overlaps with short sticks. Work top down) and insulate the floor well

This will stop stuff getting quite so covered in crap, leave gaps in the felt for ventilation, and keep the insulation close to the warm envelope of the house that is actively used.

You sure could go to the effort and expense of insulating the loft and dealing with accumulating moisture in a way that means the insulation remains effective but if you're not going to convert it to a habitable room it's money wasted imo

Yeah, I suppose it will be cheaper and easier to just fit some railings to raise the existing flooring and fit more insulation under that, as when we originally did it the recommended depth was much lower and we can do that ourselves, whereas we'd probably have to pay someone to fit insulation between the rafters as it's difficult to get up to the top of the rafters.

We might need to pay someone to fit roofing felt to the rafters for the same reason, but maybe if it's much lighter than insulation we might be able to manage it, and if we do have to pay someone maybe it will be quicker/cheaper than fitting insulation.

What do you mean by "wedge the felt open at the overlaps with short sticks"? Are you saying to cut the roll of roofing felt into sections that just span between two rafters, staple up the first one, then staple the first edge of the second section on top of the edge of the first section with a stick between them to lift the second section up a bit where it overlaps?