Number of roof fixings?

[TJLinks]

can anyone tell me of a quick way to calculate the number of roof fixing required for an above roof array? I have had a quote from my suppliers and they have included 52 roof hooks for a 2Kwp set up ( 2 rows of 5 panels)
is there a formula or a chart available????
cheers

 

[SolarCity]

Depends on many factors.

However, the roof structure itself should dictate how many roof hooks you need. The distance between the joists and wind/snow loads dictate which mounting rail to use and you go from there. 52 roof hooks for a 2kwp? Doesn't sound right to me.

 

[Markc]

That's one at under 400mm apart. Thing they may of got that a bit wrong.

Not knowing your location, roof structure, height etc can't say if it is correct or not. To many factors affect numbers of hooks and there isn't a straight forward X times Y calculation. May be speak to your installer again and ask for clarification. For all we know you could live at the top of Ben Nevis!

 

[TJLinks]

Location = Shropshire
Slated roof, only ten years old
roof timbers are approx 4" x 3" and 600mm apart

 

[TJLinks]

what would a average Number be for a good /sound roof? one every meter? one every joist?

 

[SolarCity]

It depends on the mounting system that you are using. Haven't the suppliers given you mounting data? Some mounting kits will allow you to use brackets at every 1200mm.

 

[TJLinks]

only to say it is made by Schuco, what manufacturer allows 1200 spacings?

 

[SolarCity]

Schuco do under the right conditions and with the right mounting rail. Who is your supplier?

 

[TJLinks]

Segen, not sure what the rail profile is that they are offering tho. do you know what profile rail will allow 1200? I presume there are thicker / stronger ranges and lightweight ones too

 

[Markc]

Don't know if this helps?

 

[TJLinks]

Thats a great help, thanks

 

[goodwilld]

i do every other joist but not exceed 1200mm

 

[TJLinks]

i do every other joist but not exceed 1200mm

what is your reasoning for this spacing? Do you use a formulae? also what make of rails do you use??

 

[goodwilld]

Various-Hilti and Shuco, no math on spacing just seemed strong with fixing every other one.

 

[SolarCity]

what is your reasoning for this spacing? Do you use a formulae? also what make of rails do you use??

Get hold of the Schuco documentation and it explains the maximum distance between fixings. I'd be very careful about guessing - Some rails will accept 1200 spacings and some won't.

 

[JulianC]

We use the K2 'light' rail system and the manufacturer recommends support at 1200-1400mm intervals, with no more than an 800mm unsupported section at each end. Since most rafters we come across are spaced on 2ft/600mm centres we tend to fix the rails every 1200mm. So far, nothing has fallen off the roof....

 

[TJLinks]

We use the K2 'light' rail system and the manufacturer recommends support at 1200-1400mm intervals, with no more than an 800mm unsupported section at each end. Since most rafters we come across are spaced on 2ft/600mm centres we tend to fix the rails every 1200mm. So far, nothing has fallen off the roof....

JCDC- who makes the K2 light rail system?

 

[Mark.W]

As a rule of thumb I use a bracket per meter. So if you have 5 panels in a row and the panels are say .808 wide it would come to 4.166m including the retaining clips. I would then use 4 brackets. It doesn't always work this way because of the spacings between joists etc, but that is my rule of thumb.

Hope it helps

 

[Markc]

Various-Hilti and Shuco, no math on spacing just seemed strong with fixing every other one.

Hi Goodwill,

What do you think of the Hilti system. Alex from Hilti is on the forum and has asked to meet with me via email. I just don't want to keep endless stocks of different product on the shelf.

Mark C

 

[JulianC]

JCDC- who makes the K2 light rail system?

K2 Systems in Germany. :: :: K2 Systems GmbH :: PRODUCTS

Available over here from Alternergy.

 

[goodwilld]

Hilti and Alex are good, but a bit pricey but gives you confidence, the only request i had was to give the brackets some vertical adjustment to level the rails.
I have met Alex, he was promoted to UK PV Manager and a good listener, remind me to him when & if you see him.

 

[Wiggers]

Some of the Schuco rails will allow 1200 centres. (certain conditions) With the snow we have just experienced i would play it safe and put a hook on each timber 600mm apart. Remember its your reputation on the line if it sags or collapses. Dependent on the size of panel i guess 4x6m lengths of rail will be supplied. Allow for 40 hooks. You will probably find that you trim the rails down to just over 5m and use 36 hooks thoe. Its good practice to keeps a few spare hooks on the van.