Garage roof replacement material choice

Grenage

I'd like to put solar panels on the  garage at the bottom of my garden. Our house faces North so the main roof is no use.

It's currently got corrugated asbestos cement; it will be far too brittle to move around on and I don't fancy drilling it - so I'm going to replace it.

The adjoining garages have the same material, so I should stick to something corrugated. That's likely going to mean metal or new fibre cement.

What's new FC like to work on, is it stronger than stuff that's been up a while?

born_again

I used Coroline Corrugated Bitumen Black Roof Sheets.
But I did not remove the old ones (Like yours) I built a timber frame on top & insulated between the 2 parts. Garage now gets no condensation in winter on the inside of roof, & a lot cooler in summer.

tacpot12

If you do remove the asbestos cement sheet yourself 1) make sure you know where will accept it as waste and 2) take every precaution to avoid inhaling any dust. DIY asbestos removal can be safe, but you really have to read up on and follow the process, and buy a very good mask.

Grenage

born_again said:

I used Coroline Corrugated Bitumen Black Roof Sheets.
But I did not remove the old ones (Like yours) I built a timber frame on top & insulated between the 2 parts. Garage now gets no condensation in winter on the inside of roof, & a lot cooler in summer.

That's a good idea, but unfortunately not something I can do in the current situation.

tacpot12 said:

If you do remove the asbestos cement sheet yourself 1) make sure you know where will accept it as waste and 2) take every precaution to avoid inhaling any dust. DIY asbestos removal can be safe, but you really have to read up on and follow the process, and buy a very good mask.

Aye, there's a recycling centre nearby that will take it with prior warning. I will of course take all the necessary precautions.  One's health is of the most importance.

Section62

Grenage said:

Aye, there's a recycling centre nearby that will take it with prior warning. I will of course take all the necessary precautions.  One's health is of the most importance.

If you are DIYing it then try to get a sample tested before starting work.

Not all AC boards are the same.  Some are much nastier than others.

All FC roofing products should be regarded as 'brittle' when it comes to installation and access.  Personally I'd opt for plastic coated steel with appropriate anti-condensation protection.  It is lighter and easier for DIY installation.

A key issue will be the type of solar panels you will get and how they will be fixed.  There will be issues around total mass of the roof+panels, as well as panel fixing points.  If you are getting professional panel installers involved then I'd start by asking them what their ideal installation scenario is.

If the 'adjoining' garages are actually attached to yours then achieving a weatherproof lap between the garages will be one of the most important things.  Unfortunately modern profiles won't necessarily match what is currently on the roof and the rigidity of FC means there is no 'flex' to open up or close the cover width to match the adjacent rooves.  You'd need to ensure the new sheets have the correct pitch to lap correctly on both sides.

Plastic coated steel can be supplied with flashings with sufficient 'flat' to adjust their final position to achieve the correct lap.

Grenage

Hi Section, and thank you.  I sent a sample of a few days ago so hopefully I'll hear back soon.

Plastic-coated with flashings is a good shout - I'll look into that.

I'll be doing the installation myself as I'm not bothered about the FIT on such a small install. My initial plan was to use hangar bolts to support an aluminium frame, but I have yet to sit down and do any calculations or a proper plan.

0.7mm steel will weight a fair bit less than the fibre cement, so that will help!

Grenage

Just to wrap this up:

Tests came back and it was indeed asbestos (Chrysotile).  Unfortunately the recycling centres will only take sheets about 1/4 of the size, so I would have to wet-cut them into pieces - and the centre charges would be about £380.

I have been quoted £475 for removal and disposal by an established firm, so it's a no brainer to have them take whole panels.

I managed to source plastic-coated metal sheets in 'Big 6' profile, which is the same as the old stuff.  There's only one manufacturer in the UK so it will take 4-6 weeks to arrive, but I can get them in the full length which is ideal.

I won't be replacing the asbestos end pieces that fill the corrugation, so there should be plenty of breeze to combat condensation.

The replacement is substantially lighter, which will more than cover the planned installation.

Thanks for your advice.

Section62

Grenage said:

I won't be replacing the asbestos end pieces that fill the corrugation, so there should be plenty of breeze to combat condensation.

I wouldn't rely on ventilation alone to avoid condensation - either specify the steel with bonded anti-condensation fabric, or else use something like celotex (25mm should be enough) to insulate the steel and provide a continuous layer to carry any condensation down to the eaves (tape the joints on the upper surface so the water drains).

Personally I like the celotex approach as it makes the space a little warmer and nicer to use in the winter, and the silvery foil helps reflect light so makes the space look brighter (/easier to light).

Either is easier to do when the roof is being put on - retrofitting is a PITB - hence I'd take one or other of the options automatically rather than waiting to see if there is a problem.

Grenage

Hi Section,

Alas the anti-condensation lining wasn't an option with one the place that could supply the sheeting.  I'll take your experience over my optimism, but I suppose the extra height might pose an issue with joining it to the neighbour's garage?

What about a full-width piece of DPM stapled across the wall plates and joists before the roof goes on? I could then put celotex between the joists as a little insulation.