Mounting Solar A Frame to flat roof.

[Crispin]

Hi Folks,

I will be putting some solar panels on my flat roof. As it is not ideal to have them flat, I want to build a small AFrame for them. My question is how to mount this to the roof.

I cannot get in the cavity unless I rip the ceiling off. The roof is, I guess, rather think plywood. I can walk on it (all 16 stone of me) without any flexing underfoot.

Is there an easy way of finding the joists without exploratory drilling?

As for the AFrame, I intend having two 50mm angle iron secured to the roof, the aframe will thing bolt to this. This allows me to use many mounting points to spread the load.

As for load, as the panels will be at an angle, they could act like a giant wing and generate a considerable amount of lift. I suspect the roof sheets are simply nailed in which would not be strong enough. Or will it? I could put a deflector on the high (open) side which would negate this effect.

As for the details: It's a new extension (About 5 years old, not done by me) Roof is most definitely wood with felt on top. Is flat and basically horizontal. Structurally, I have no more information on it.

The panels are 1400cm long and will sit at about a 30 degree angle making the high side 750cm. The width of each panel 900 so with gap, call it 100. I plan on having 6 in the end. So each bottom bracket, 2 of them, will be 6M long. That's many many mounting points. Spread the load. Best way to water proof that? Douse with bitchimin?

[Crispin]

Meant to add...

Thanks in advance.

Cheers, Crispin

[David Hansen]

On Tue, 19 Aug 2008 07:43:22 -0700 (PDT) someone who may be Crispin wrote this:-

Making holes in roofs is never a good idea if they can be avoided, even on a pitched roof. Making holes in flat roofs is a double plus ungood idea.

Could you make two U shaped rails which would be fastened to the walls either side of the roof? With the pipes going via the wall so no holes in the roof?

If you really do want to make holes in the roof then I suggest removing some or all of the felt, in order to install a wooden upstand which fastens directly to the plywood. The precise design of this upstand depends on circumstances. Re-use the existing felt or use new felt to cover this upstand and use new felt in the middle of the upstand. Then fasten the rails to this upstand. Not a solution I would look at first.

[Chris]

David Hansen wrote in news: [e-mail]:

A common means of doing this is to make a square angle iron base with angle or T steel dividers suitably spaced so you can place concrete blocks on angle irons L shaped base.

I am sorry if I am not being clear it is easier to imagine than explain

Chris

[Andy Dingley]

I presume "think plywood" is the stuff that you think is thick until your foot goes through it, then you realise it was thin.

[Crispin]

Thanks for the ideas folks.

David, Making holes in the top of a flat roof is the last thing I want to do... After having another think about it, the panels will eventually take up most of the roof width. This means my bracket might as well go down the side of the roof and fasten to the beams in the walls. I will remove some tiles over the weekend to take a peek. (Weatherman says I have a 30 minutes window of no rain) This would have a slight advantage or moving the lateral loading to the walls and not the roof. Also no lift acting on the roof.

Chris: I kind of think I know what you mean but not overly excited about putting concrete on my roof. (Or did I miss it?)

Andy: I've been on it many times and have not felt like it would give. I have a good knowledge of that feeling. Twice I have fallen clean through. Once as a kid running on a tiled roof. Through the roof and ceiling. Luckily the floor was there to break my fall. Second was simply through the ceiling onto my dog who was following the footsteps from below. I don't plan on any more...

What are the regs for building a roof? Am I save in putting a spread load of about 100kgs on it? I suppose so as I weigh, cough, more than that...

Are the rafters simply nailed to the upright beams or secured in a way that they cannot pull up? If so, a simple bracket would work.

Thanks Again

Cheers, Crispin

[Chris]

Crispin wrote in news:04f01c38-e163-44fe-a066- [e-mail]:

Sorry if i was not clear I wasn't suggesting you cast concrete blocks but use concrete building blocks also once known as breeze blocks making sure the base frame spans the roof joists so spreading the load preferably placing it toward the supporting wall rather than the centre of the roof Chris

[David Hansen]

On Wed, 20 Aug 2008 03:00:15 -0700 (PDT) someone who may be Crispin wrote this:-

I don't quite follow beams in the walls and tiles, but that doesn't matter as it depends on the peculiarities of the building concerned.

Remember to fasten any brackets low enough down the wall that the mass of the wall will be able to resist any forces. Otherwise it will suffer the fate of bodged aerial/satellite installations which are placed too high up the wall. The wind forces will be greater than for a satellite dish.

Also ensure the bracket is stiff enough not to vibrate excessively.

I would still rather do this than make holes in a flat roof.

If there is a vertical wall above the flat roof could you use one bracket and connect the top of the panels to the wall?