Reinforcing Loft Joists for Storage

[BillyWillySilly]

We just had a loft ladder installed to the second-floor office area. Room was plenty cold and I suspected no insulation above and I was right. Now the hatch and ladder is fitted, the carpenter pointed out that the joists were not particularly strong. They measure just shy of 3" x 2" with a span of 3.1m. Room length is 3.5m in the loft spread over 10 joists. Centers vary though - house was built in 1902 and the extension possibly at the same time. Joists range from 32 to 35/36cm mostly.

I would like to insulate and board for some light storage - guitar cases, xmas lights and as the height is at a premium, was thinking of using 75mm PIR between the joists. Not sure if there's enough height for loft legs though.

My main concern is how strong the joists are for boarding and storage. The carpenter has reinforced the hatch. My question is whether I need to go further? I found this post that diagrams new 4" x 2" joists glued and screwed to the old. Would this be required? I'#m partial to this mainly as it would give me a usable 17cm of insulation below the boards with an air gap.

 

[blup]

Increasing the depth of the joist strengthens it.

Blup

 

[BillyWillySilly]

So this method?

 

[cdbe]

I would accept the hit on headroom and insulate to current standards (Probably something like full fill mineral wool between the raised joists and 100mm celotex on top (in the area you want to board, with more mineral wool at the eaves - celotex is very expensive). As it's only for storage, you can lay the celotex directly on top of the joists and just lay thin plywood or OSB on top to form a "floor". Have a look at 9mm OSB in Wickes, probably the cheapest solution and comes in 600mm wide lengths that should fit through your hatch.

I would also investigate that insulation in the rafters, I'm not sure what it is but it probably shouldn't be there (affects ventilation of the roof timbers).

 

[BillyWillySilly]

I would accept the hit on headroom and insulate to current standards (Probably something like full fill mineral wool between the raised joists and 100mm celotex on top (in the area you want to board, with more mineral wool at the eaves - celotex is very expensive). As it's only for storage, you can lay the celotex directly on top of the joists and just lay thin plywood or OSB on top to form a "floor". Have a look at 9mm OSB in Wickes, probably the cheapest solution and comes in 600mm wide lengths that should fit through your hatch.

So no additional timber - just insulation with OSB loosely laid on top? With the joists being close together there is some strength but no need for additional noggins?

 

[cdbe]

raised joists

I would add the timber on top of the existing as per your suggestion/drawing, technically noggins as well but I think it would be ok without for light storage.

 

[BillyWillySilly]

Thanks! I'll get some timber ordered.

 

[mrrusty]

What I have done in a similar space is to roll 100mm loft insulation which compresses to 75mm - yes I know it loses a bit of efficiency, but still good - then cross-joists at 90 degrees with 4x2 with another layer of 100mm insulation, then chip flooring. Makes a rigid floor.

 

[BillyWillySilly]

What I have done in a similar space is to roll 100mm loft insulation which compresses to 75mm - yes I know it loses a bit of efficiency, but still good - then cross-joists at 90 degrees with 4x2 with another layer of 100mm insulation, then chip flooring. Makes a rigid floor.

Why is the diagrammed method recommended over what you suggest?