Getting panels straight

Hi i’ve been a single ply membrane installer for 10 years. I have just started installing topdek panels, which are a composite panel with decking, insulation and membrane.
Just wondering if anyone has any tips on getting the panels to run straight across the roof.
I start of by getting the sheets parallel to the upstand by taking a measurement of the structural steel but by the time i get to the other side the sheets have run out 50mm.
I’ve tried using a 3 4 5 triangle but i still find i have to try and adjust the panels as i go to get them at a right angle to the eaves.

Sometimes, you have to snap a chalk line and cut off to get a straight edge.

I don’t know of the product you mentioned, but I am sure its the same as with insulation board.


The boards are probably square (jigged @ the manufacturer), it’s the building that is off.


I can understand how they are hard to keep in line. Since they are not laid in place like we are used to.

They tell you to keep ajusting as you go. So it seems like a learning curve that everyone goes through.

Like the others, I’m not familiar with the product, but as mentioned I suspect the building is not square.

As for the 3, 4, 5, triangle, have to tried increasing the size of your triangle?

Just FYI. It is a simple right triangle measurment which can be any number. Just plug the number you need to measure and it works just fine. A square, plus b square, always equals C square.

I very seldom find a perfect square home. It really is evident when on a sheet metal install. We use some tricks for lining up homes. We will start by using a couple of panels, lap jointed without field fasteners. Square it up and then plug’em.