Laying floor in attic - attaching joist to rafter?

[Pinkmargera]

Hello,

I would like to build a floor in the attic for some lighter storage (Christmas decorations, sleds, etc.) and I'm wondering if the following solution is possible.

Currently, there is a catwalk in the attic and about 40 cm of insulation. The insulation consists of overlapping layers of boards. The trusses are spaced at 120 cm and are partially covered by insulation.

Since I don't want to build up from underneath the trusses, I'm considering if it would work to place a 45x70 beam across the truss (attached at four points and resting on the catwalk) and then lay tongue and groove boards on these. Is this okay from a structural standpoint?

That is, roughly like the sketch below showing half the side (beam in blue, tongue and groove boards in green). Note that this is an old image where the insulation was removed to show the entire truss.

 

[Titagurgi]

Placed 45x70 on its edge.

Attached outer panel since I had 1 m pieces at home.

 

[Pinkmargera]

Placed 45x70 on edge.

Installed outer panel as I had 1 m scraps at home.

What do you mean, did you place 45x70 on the bottom chord of the truss?

I would preferably avoid building from below due to potential thermal bridging.

 

[Titagurgi]

What do you mean, did you put 45x70 on the rule at the bottom of the truss?

I would preferably avoid building from below due to the possibility of a thermal bridge.

On the truss, across.

 

[Pinkmargera]

On the truss, across.

On the truss, across.

Ok, I have two layers of insulation over the bottom frame and cannot place it that way. That's why I wondered if it is possible to attach to the diagonals, or if it must be supported from the bottom frame.

 

[Isakare]

Build on, it will work fine. Several houses in my area have done so, we have the same type of roof trusses and 20 cm spray insulation over the underarm.

 

[Pinkmargera]

Build on, it will work fine. Several houses in my area have done so, we have similar trusses and 20 cm spray insulation over the underarm.

Ok, that sounds good! How many screws should you attach in the diagonal - is two in each enough?