Lining and insulating loft before/after getting solar panels installed

[Why Not Indeed]

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?

Pretty sure he's suggesting it be fixed up horizontally, rather than 1 sheet fixed by its long edges along 2-3 rafters.
Horizontally means that the overlaps are not fixed down tight together. You do not want to be trapping moisture in there.

 

[robinbanks]

roofing felt to the rafters for the same reason

Roofing felt these days is a plastic membrane similar to the material more upmarket bags-for-life is made from, not the heavy, thick black bitumen roll of days of old

You'd measure a length of membrane the full width of the roof at the top and cut it, then offer it up and staple it in place but not so it's guitar string tight. Staple it to every rafter
The next length goes below it so you work down from the top of the loft and the lengths of membrane overlap by about six inches, again not tight
Now, in your mind, go to any part of the membrane between two rafters. At the overlap, push the upper membrane towards the tiles and pull the lower one towards you, creating an opening that is like a very wide, not very high diamond shape and wedge something in it so it remains open. Do this with many places.

This means you have a ventilated loft space but any dust and dirt falling it most likely to remain on the tile side of the membrane

Modern roofing felts are water vapour permeable, and any condensation forming on the underside of the membrane should soak through and evaporate away from the other side so this creating-openings shouldn't strictly be necessary, but I think most people that create structures to deal with moisture laden air would go belt and braces on it and arrange to maintain the ventilation a loft has had its entire life

 

[Why Not Indeed]

Roofing felt these days is a plastic membrane similar to the material more upmarket bags-for-life is made from, not the heavy, thick black bitumen roll of days of old

I did wonder why you appeared to be suggesting something not moisture-permeable for this task. Also eminently un-suited to stapling to the underside of anything!

 

[Derek M]

Roofing felt these days is a plastic membrane similar to the material more upmarket bags-for-life is made from, not the heavy, thick black bitumen roll of days of old

You'd measure a length of membrane the full width of the roof at the top and cut it, then offer it up and staple it in place but not so it's guitar string tight. Staple it to every rafter
The next length goes below it so you work down from the top of the loft and the lengths of membrane overlap by about six inches, again not tight
Now, in your mind, go to any part of the membrane between two rafters. At the overlap, push the upper membrane towards the tiles and pull the lower one towards you, creating an opening that is like a very wide, not very high diamond shape and wedge something in it so it remains open. Do this with many places.

This means you have a ventilated loft space but any dust and dirt falling it most likely to remain on the tile side of the membrane

Modern roofing felts are water vapour permeable, and any condensation forming on the underside of the membrane should soak through and evaporate away from the other side so this creating-openings shouldn't strictly be necessary, but I think most people that create structures to deal with moisture laden air would go belt and braces on it and arrange to maintain the ventilation a loft has had its entire life

Thanks for the detailed explanation. That sounds fairly easy.

If the felt is fairly lightweight, when doing the higher parts we might be able to have one of us hold the felt against the rafter with a long pole/gripper, whilst the other person staples it in place with a stapler on a long pole. Might have to Macgyver something together to do that, but it's probably easier (and safer) than trying to get a ladder up in the loft and then balancing it against one of the rafters.

Otherwise we might just do the lower parts that we can reach and then pay someone to do the upper parts.

The scaffolding to install the solar panels went up on Friday, so they should be getting installed next week and the installers should be able to confirm whether there's any lining behind the tiles then, although I guess that won't really affect whether we fit this extra felt lining.

 

[Derek M]

Are there still different types of roofing felt?

This one is described as polyester https://www.amazon.co.uk/dp/B09X72BCQS/ and weighs 18kg per 10m, and this one is a lot cheaper and weighs about the same but says it's bitumen https://www.wickes.co.uk/IKO-Green-Mineral-Shed-Felt-Roll---10-x-1m/p/164174

I understand that bitumen is produced through the distillation of crude oil, and this page says that it has to be bonded with fire so is not suitable for DIY (not that I'd let anyone use a blow torch in the loft!) https://www.roofingmegastore.co.uk/blog/torch-on-vs-self-adhesive-felt.html

 

[robinbanks]

Otherwise we might just do the lower parts that we can reach and then

Just to point out, you do the top first

"Felt" as a search term won't bring many relevant products these days, sorry. You're looking for breathable membrane

Onduline Ondutiss Air 100 Breathable Membrane - 50 x 1.5m | Wickes.co.uk

Onduline Ondutiss Air 100 Breathable Membrane - 50 x 1.5m

www.wickes.co.uk

This isn't a recommendation to use that particular product, from wickes, it's just to give you an idea of what kind of thing you're looking for. I see Cromar vent3 being used a lot (used it on my roof last year) https://www.ebay.co.uk/itm/202474311676

 

[Derek M]

Just to point out, you do the top first

"Felt" as a search term won't bring many relevant products these days, sorry. You're looking for breathable membrane

Onduline Ondutiss Air 100 Breathable Membrane - 50 x 1.5m | Wickes.co.uk

Onduline Ondutiss Air 100 Breathable Membrane - 50 x 1.5m

www.wickes.co.uk

This isn't a recommendation to use that particular product, from wickes, it's just to give you an idea of what kind of thing you're looking for. I see Cromar vent3 being used a lot (used it on my roof last year) https://www.ebay.co.uk/itm/202474311676

Oh yeah, I did understand that you were saying to start at the top so that the falling dust is trapped behind the membrane and doesn't escape through the gaps where the sections overlap and I explained this to my Dad, so I don't know why I said in my post that we might just do the lower parts ourselves and then get someone in to do the higher bits.

Thanks for clarifying that I need to look for breathable membrane. Those products are a lot cheaper than the stuff I was looking at, which my Dad will be happy about and probably one 50m roll will be enough to cover all the rafters, two at most.