How to mount PV on sloping mineral felt roof?

[jerriais]

Hi,

Got a customer with a sloping felt roof, about 22 degrees. So this is basically the same covering as a flat roof but not possible to use any of the normal flat roof mounting methods. My best idea so far is to mount with normal roof hooks well sealed with silicon where we screw them down through the felt to the rafters then torch on another piece of felt covering the base of the roof hook. Anybody ever done one of these before? Any better ideas?

Thanks,

Matt

 

[solarsparkie]

make friends with a local flat roofer and a metal worker ( ideally they should have thier own tool maker ) they got us out of some tight spots when kit was unavailable . The flat roofer gains loads as you will be able to pass him on remedial work needs to be done prior to installation so you will find them more than willing to help

 

[solarsparkie]

ill post a picture of a custom installation later this week need a nice day as its going on our website , couldnt be done with standard off the shelf mounting kit you will be amazed at the amount of talented people out there

 

[northernsun]

I've done one quite similar and ended up fixing lengths of timber down and then hot felting over them. The timber goes down where the fixings will go, then put fixings onto the timber and fixed the rail. Seen this done with hanger bolts, angle brackets and flat slate fixings with roof felt over them.

 

[Worcester]

We've got one to do next week 20° felted roof, support structure well solid, I have a couple of ideas, - anyone any description or photo's of how they did it? Thx

 

[Gavin A]

hanger bolts and butyl mastic.

seriously, even the spurious objections around the potential for broken slates don't apply, and it's neither a tile nor a slate roof, so is allowed under MCS rules.

 

[Worcester]

Thanks Gavin, I'm still not to happy of hanger bolts into 38mm trusses - and the thought of then nogging or strengthening them all up just to take a hanger bolt - we did consider it though as I've got a few hundred in the store from the fibre cement roofs we do every now and then.

So we're considering either:
(1) Slate roof hooks with edpm under and then bitumen flashing over
or
(2) K2 Flat rail cut into 750mm lengths so it spans two rafters with edpm under the mounting points and flashing over and the water will flow between the cut sections (in prinicpal a bit like the K2 minirail Mounting systems for solar technology: > Solar mounting > Sloped roof systems > K2 MiniRail System )

I think (1) will be the neatest solution

 

[solarsavings]

We did one last week on a block of stables. It had just been re-roofed...............................................badly. Anyway, we used slate hooks and stixall. We've done a few like that and not had a problem.

 

[Gavin A]

Thanks Gavin, I'm still not to happy of hanger bolts into 38mm trusses - and the thought of then nogging or strengthening them all up just to take a hanger bolt - we did consider it though as I've got a few hundred in the store from the fibre cement roofs we do every now and then.

we'd never use them directly on 38mm trusses either.

It's actually really simple process though to do it using noggins, as you can have one person outside drilling the holes in a line where they're wanted, then another inside positioning the noggins relative to the holes, while the person outside goes back and starts at the first noggins, drills a pilot hole, then fits the hanger bolt.

We did 15 kwp like this with all bolts installed in a day - I think we had 3 people on the bolts, 1 outside, 1 inside fitting noggins, 1 inside measuring and cutting the noggins.

 

[solarsavings]

Photo isn't very clear but you should be able to make out the hooks. I think you get a better seal with them and stixall in a situation like that.

 

[Gavin A]

was that fixed to the rafters, or to the ply?

 

[solarsavings]

Through the felt/22mm sterling board into the 38mm rafters which are tied to the walls with once turned straps.

 

[Worcester]

This is a proper roof, properly done about 3 years ago and in very good condition so will easily last 20 years, with proper solid trusses, and is a 'habitable' building - youth / drop in centre used every day and night - we're doing a full eco retrofit on it, insulation, air-air heat pumps etc etc, so roof integrity is critical

My leaning is towards the slate hooks with 6x80 mm S/S Spax (SPAX® Stainless steel Washer Head T STAR screws - 6.0 x 60 - 200pcs ) and then flash over them (maybe even hot flash them). Positioning the hooks is straightforward enough - 3mm pilot hole from inside out for the first and last rafter and then measure accurately for the in-between hooks.

- - - Updated - - -

This is a proper roof, properly done about 3 years ago and in very good condition so will easily last 20 years, with proper solid trusses, and is a 'habitable' building - youth / drop in centre used every day and night - we're doing a full eco retrofit on it, insulation, air-air heat pumps etc etc, so roof integrity is critical

My leaning is towards the slate hooks with 6x80 mm S/S Spax (http://www.simplyspax.co.uk/spax_washer_head_screws_/stainless_steel/stainless_steel_m6/spax_stainless_steel_washer_head_t_star_60_x_080_100pcs_P1153.html ) and then flash over them (maybe even hot flash them). Positioning the hooks is straightforward enough - 3mm pilot hole from inside out for the first and last rafter and then measure accurately for the in-between hooks.

 

[a1colly]

Flat bracket, CT1 in the pilot hole for fixings. EPDM rubber underneath bracket and then acropol over the top of everything. Done a few like this and never had a call back.

 

[The Solar King]

Jual, a Danish company do a really good fixing for just this application. Can be specified with different makes of felt to suit and hopefully not invalidate the warranty of the covering. Not cheap but pull out is huge so you don't need many per sqM. Not sure what position is with MCS012.