Loft floor leg alternative strengthen structure?

[JamToday]

Hello all,

Currently part of my loft floor is boarded with only 10cm of insulation underneath. The rafters are 7.5cm deep so insulation in this area is compressed.

I have enough off cuts of fence posts and enough gravel kick boards in garage to cut up and create a structure to support the existing boards and allow for 17cm of insulation plus 5cm air gap. I plan to sandwich post offcuts (positioned to meet the existing roof structure) in between the gravel boards and fix the existing boards in top.

So more in the style of loft zone type solution.

Was going to run the new structure at 90 degrees to the existing.

My questions are:

Given the existing structure is only 75cm deep do I need to retrofit noggins? If so what's the easiest / quickest way to accomplish this?

Should I be concerned about creating a cold bridge (excuse me if this is not quite the correct term) and if so how should I prevent this?

 

[blup]

No idea if the existing roof joists are adequate. One way would be to glue and screw new cls battens on top i.e. to increase the overall depth of the joists making them stronger. You may have to factor in services or other roof woodwork like binders. I personally would avoid fencing timber which may warp or be damp.

If your only use the loft for christmas decorations, why not just get the insulation in and lay a few boards loose at first.

Blup

 

[JamToday]

Thanks @blurp

No idea if the existing roof joists are adequate. One way would be to glue and screw new cls battens on top i.e. to increase the overall depth of the joists making them stronger. You may have to factor in services or other roof woodwork like binders. I personally would avoid fencing timber which may warp or be damp.

If your only use the loft for christmas decorations, why not just get the insulation in and lay a few boards loose at first.

Blup

That's a good point RE warping I hadn't given that enough consideration.

The loft was boarded out in this way when we moved in and it's a bit more than x mas decorations, although have reduced clutter by a lot recently.

Should the cls battons you suggest cover the full span of the roof or just the portion I am adding boards to?

Are you suggesting that the battons are tall enough to accommodate the second 17cm of insulation?
Or that I forget about the additional 17cm of insulation?
Or that I add in the battons to strengthen the existing and add loft legs (Or 17cm cls at 90 degrees) on top?

 

[RandomGrinch]

Should the cls battons you suggest cover the full span of the roof or just the portion I am adding boards to?

It's up to you, but I have recently taken this advice from Tony1851.

Strengthening Loft floor

I am looking into having my loft converted for storage. I want the floor boarded, roof plasterboarded and loft ladder installed. The loft currently is full of a lot of boxes possibly 100kgs worth. I have had someone come round to quote for the work and they have advised me ''that...

www.diynot.com

I've strengthened my 3x2 (quite bowed) joists. I've also installed 270mm insulation and a storefloor above (which I'm very happy with). The loft boarding is now rigid and the space is far more usable

 

[blup]

Good advice

Blup

 

[Tigercubrider]

I made I beams by using OSB strips with 2x1 screwed to the long edges.
They are roughly 8” high and once the loft boards are screwed down it’s plenty strong enough

 

[JamToday]

It's up to you, but I have recently taken this advice from Tony1851.

Thanks, @RandonGrinch The advice makes sense, but how does the 4" on timber (or 10cm) allow for 17cm of insulation plus an air gap between insulation and boards?

 

[RandomGrinch]

I put 100mm between the joists and 170mm perpendicular, over the top. The Storefloor lifted the boarding above that (279mm for the standard height).
When I thought about it later, I should have put 170mm between the joists too.

 

[JamToday]

I put 100mm between the joists and 170mm perpendicular, over the top. The Storefloor lifted the boarding above that (279mm for the standard height).
When I thought about it later, I should have put 170mm between the joists too.

By between, I assume you mean fixed on top as described by Tony1851?

Sounds like a lot of weight, what timber did you use?

 

[cdbe]

Ceilings don't have noggins, but they often have binders and you shouldn't interfere with them if you find any. It's not clear whether you want to increase the load carrying capacity of the loft or insulate it better or both

I don't quite follow your "sandwich" of fence posts and gravel boards and whether these are to be fixed to the roof? If you're happy with the existing capacity (often just keeping the heavy items well away from mid span is enough) and your focus is insulation then you want to reduce the thermal bridging of the timber/interruption to the insulation - which is what the loft legs do - so you could use the fence post offcuts in the same way - they'd need to be fixed to the existing joists eg by some long diagonal screws.

You don't need an air gap, and you should consider more insulation if at all possible (450mm is the new 300mm!).

 

[JamToday]

Ceilings don't have noggins, but they often have binders and you shouldn't interfere with them if you find any. It's not clear whether you want to increase the load carrying capacity of the loft or insulate it better or both

I don't quite follow your "sandwich" of fence posts and gravel boards and whether these are to be fixed to the roof? If you're happy with the existing capacity (often just keeping the heavy items well away from mid span is enough) and your focus is insulation then you want to reduce the thermal bridging of the timber/interruption to the insulation - which is what the loft legs do - so you could use the fence post offcuts in the same way - they'd need to be fixed to the existing joists eg by some long diagonal screws.

You don't need an air gap, and you should consider more insulation if at all possible (450mm is the new 300mm!).

Understood RE binders.

I want to beef up insulation to 27cm as a minimum (to match the rest I have added to the loft). I want to add boarding on top to take light storage xmas decks etc (which are already up on the existing structure in all fairness).

I have lapped sarking felt and enough vents fitted but am seeing some condensation issues even so. From what I have read too much insulation can make condensation worse so I want to be careful and stick to the 27cm.

My idea was to use the posts but form a structure at the base and top of each with gravel boards cut-down lengthways (a bit like a pallet). However, I do see that warping might be an issue. I guess they could be left unfixed to the roof thinking about it.

 

[RandomGrinch]

By between, I assume you mean fixed on top as described by Tony1851?

Sounds like a lot of weight, what timber did you use?

Sorry if I caused confusion, I was talking about the insulation.

put 100mm between the joists and 170mm perpendicular, over the top

As said by others, you don't need to do much to just achieve extra insulation.

In my case I wanted extra strength for the loft storage, given that my joists had 130 years of bow and some other damage. I also wanted more insulation.
I don't know if these work-in-progress pictures show much:

So following Tony1851, I screwed and glued 2x3 CLS on top of the existing 2x3 joists.
I added 100mm of insulation between the joists and 170mm perpendicularly over the top - disposing of all the existing insulation and vacuuming up the detritus.
And Loftzone Storefloor went over that.

The floor is now solid and a very usable space.

 

[JamToday]

@RandomGrinch thanks for taking the time that makes perfect sense.