Question about weight of raised loft floor

[IrishPhil]

A big thank you to everyone who has posted about raising a loft floor with counter-battens to achieve an acceptable thickness of insulation. I spent about 4 hours reading old posts this past weekend before going out and buying my materials. But now I'm worried...! I took delivery of the timber, flooring and insulating batts this afternoon, and the weight of everything added together seems massive, and by my rough calculations could be over 300 kg.

My 1940's house has 3"x2" joists in the loft, spanning 5m, at centres ranging from 11" to 14". I have bought 200x47(mm) timbers which I intend to run at 90deg across these, over an area of about 12 m^2. (The area is purely for storage - ski gear, old books, suitcases etc.) There are 3 internal brick walls under this area - one at each end and one about 1/3 of the way along - though my new joists will not be resting on these, as the old joists are higher than the brick. (I hope that makes sense!)

My questions:

1. Is a load of 25kg/m^2 acceptable (and that's before I put any items in the loft)? Considering I have had my 100kg stepping from joist to joist from time to time I'm maybe worrying about nothing, but if there's anyone with more experience I'd be glad to hear from you before I cause my ceiling to come in!

2. Could/should I build up above the internal walls to the same level as the old joists, thereby getting the walls to take the brunt of the load? How would I do this?

All advice will be gratefully received, thanks.

 

[big-all]

so what is the maximum span where they are neither supported underneath or screwed to the roof structure!!!

 

[Deluks]

Cross battens shouldn't be any more than 2x2 really. your timbers are too big for cross battening, unless you rip them down to size. In any case 3x2 is pretty flimsy for anything useful. As you've now stumped the cash you should consider fixing the 8x2's from wall to wall, sitting higher than the existing joists which really shouldn't have any extra loading on them. You can fix timber blocks or bricks onto the supporting walls, between the existing joists. To raise the new joists up above the loft side of the ceiling (in case plaster, screws and other crapola get in the way)

You could also just attach your 8x2's to the side of your existing joists, screwing or bolting all the way along the length, but each end of the new timbers must be located onto a suitable bearing.

Search the forum for 'sistering'


Edit* just re-read about the wall picking up 1/3 of the span. Doesn't sound that bad now, but proceeding with my advice above would be a better way to do things.

 

[TrevorMcAlister]

Hi
In the next couple of weeks I will be undertaking the same task as IrishPhil of raising the loft floor, so I can add 170mm of rock wool insulation and board the loft using old floor boards to create a storage area.

My house was built in 1939 but a little smaller than Phil’s, with 4”x2” ceiling joists spanning 4.1m. Total length of the house is 11m, again with 3 block built internal walls that divide the bedrooms & stairs.
I pretty confident that it will be structurally sound placing the new 2”x8” joists at 90deg on top of the existing ceiling joists.

I was just after any tips that Phil could give me once you get started. I have already realized that it’s a good idea to create an over sized loft hatch (0.8mx1.5m) to make getting the 2”x8”x3-5m up into the loft easer.
Trevor