Loft storage weight question

[bm58xsc8]

I know questions like similar to this have been asked dozens of times before but... I do have some specific questions.

I've read that the recommended weight limit for loft storage is 25kg per m2. I have seen some posts go up to 50kg. I imagine that there a lot of this is going to depend on the variation in house build quality.

I live in a new build , the loft is about 6m x 6m (pic attached) and the joists are about 34mm x 94mm and roughly 60cm apart (although that varies). Given that, I expect I'm towards the lower end of the storage recommendations.

I was thinking of boarding using loft legs and 18mm OSB boards. Problem is, 18mm OSB boards themselves weigh 11-14 kg per m2. Add to that the weight of the loft legs and I think that means I only have about 10-12kg per m2 of storage weight.

That makes me think the usefulness of loft storage is pretty limited. Have I missed something?

 

[freddiemercurystwin]

The roof won't collapse, after all during construction it coped with some 16st fat ass builders walking about on the trusses. The order of the day is to just be sensible, Christmas decks, suitcases no worries. That said I lived in a new build about 20 years ago (they're no worse or better now for strength) and stored all-sorts of ridiculous stuff up there, 25kg speakers, massive boxes of junk and filing, the roof was crammed in the middle section, I'm still alive.

 

[bm58xsc8]

Thanks for the reply. I'm still unsure about exceeding the 25kg recommendation. I guess I'll be storing very light stuff up there. 10kg/m2 is not a lot.

 

[JohnD]

Rather than loft legs, I prefer counter-battens, laid at right angles to your existing timbers and skew-screwed to them. This will spread the load and add rigidity. If you top it with a ply floor, also screwed down, this will add even more rigidity. I used decking timbers, which are pre-treated and quite cheap.

You can double up the battens down the middle where you will mostly be walking and standing if you like. Use 600mm spacing so you can easily lay insulation between them.

Do not use nails and hammers or you will crack the ceiling plaster.

 

[robinbanks]

10kg/m2 is not a lot.

Upgrade the supports then!?

 

[bm58xsc8]

I have seen some people, particularly professionals, do it that way. But doesn't this compress the insulation; reducing thermal efficiency and causing mould? It's my understanding that there should be 27cm for the insulation, plus a gap to let air circulate between the loft boards and the insulation.

Rather than loft legs, I prefer counter-battens, laid at right angles to your existing timbers and skew-screwed to them. This will spread the load and add rigidity. If you top it with a ply floor, also screwed down, this will add even more rigidity. I used decking timbers, which are pre-treated and quite cheap.

You can double up the battens down the middle where you will mostly be walking and standing if you like. Use 600mm spacing so you can easily lay insulation between them.

Do not use nails and hammers or you will crack the ceiling plaster.

 

[bm58xsc8]

Upgrade the supports then!?

That's interesting. How would you go about that? Is it just a case of adding more joists?

 

[JohnD]

If you feel you need 250mm of insulation, and you existing timbers are about 100mm deep, you can add 150mm or so of counterbattens, or loft legs which do not give such a strong floor. You do not squash the insulation, you run it between the timbers. There is also a slight gain from the surfaces of the floor.

Thicker insulation gives diminishing returns, as it is cutting from an already reduced figure.

For example if your heat loss was one kW, and the first 50mm halved it, it would save you 500W

If your next 50mm halved it again, it would save you an extra 250W

Then 125W, 64W, 32W for each addition 50mm of thickness.

So in my example, increasing from 200mm to 250mm would save you an additional 32W from your original, uninsulated 1000W

(Figures made up for simplicity)

 

[freddiemercurystwin]

As above, no need to compress the insulation that's the whole point of the new joists, there are also systems like loftzone: https://www.homebase.co.uk/loftzone-storefloor-kit-medium/12810020.html or there are the dreaded loft legs.

You can also gain additional storage with shelving built on the trusses:

 

[Mister Banks]

I'm adding an extra 170mm of insulation to my loft so I will have a total of 270mm of insulation. If I buy 170mm joists for the loft boards they will be adding quite a lot of extra weight. Loft legs don't get much appreciation but at least they are relatively light.

 

[freddiemercurystwin]

Though you're adding less weight you're also not spreading the load onto the adjacent joists.

 

[Mister Banks]

Though you're adding less weight you're also not spreading the load onto the adjacent joists.

True but how much would five 2400mm x 170mm x 50mm joist weigh, plus of course the weight of the loft boards, probably more than the items being stored.

I'm still undecided between joists and loft legs.

 

[freddiemercurystwin]

It's up to you, it really won't make a heap of difference so just do what you're most comfortable doing, as mentioned I've stored heaps more than 25kg/m2 in a trussed loft and lived to tell the tale. I stored a whole lot more in the loft in our last house and reading some of the threads on this forum I should not be alive. I am a walking miracle.

 

[bm58xsc8]

It's up to you, it really won't make a heap of difference so just do what you're most comfortable doing, as mentioned I've stored heaps more than 25kg/m2 in a trussed loft and lived to tell the tale. I stored a whole lot more in the loft in our last house and reading some of the threads on this forum I should not be alive. I am a walking miracle.

I'm not worried about dying, I'm worried about my girlfriend being angry with me, which is much much worse.

 

[bm58xsc8]

If you feel you need 250mm of insulation, and you existing timbers are about 100mm deep, you can add 150mm or so of counterbattens, or loft legs which do not give such a strong floor. You do not squash the insulation, you run it between the timbers. There is also a slight gain from the surfaces of the floor.

Thicker insulation gives diminishing returns, as it is cutting from an already reduced figure.

For example if your heat loss was one kW, and the first 50mm halved it, it would save you 500W

If your next 50mm halved it again, it would save you an extra 250W

Then 125W, 64W, 32W for each addition 50mm of thickness.

So in my example, increasing from 200mm to 250mm would save you an additional 32W from your original, uninsulated 1000W

(Figures made up for simplicity)

Sorry John, I don't quite get it when you say that "you don't squash the insulation, you run it between the timbers".
If the counterbattens run perpendicular to the original joists I can't see a way of running the insulation between them without there being some compression.
Have I misunderstood what you meant?