Loft boards 12mm or 18mm?

[Builder2011]

Good morning.

Are 12mm thickness chipboards adequate for a new loft floor? The 12mm boards add a weight of 7.17 kg psm.

18mm boards with tongue and groove (which do not have to join specifically on centres of the new joist) are much heavier at 12.8 kg psm.

Over a loft area of 32.2 sm, the 12mm boards would add a weight of 230kg. The 18mm boards would add a weight of 412kg.

The new joists are at 360mm centres.

Has anyone put in 12mm boards at these centres?

 

[abuildingsite]

In 2003 the LDSA (London District Surveyor's Association) agreed the following after Part E (Sound) was revised:

'The new flooring, should be a minimum 21mm thick chipboard or equivalent, of minimum 15 kg/m2 density and screwed with occasional screw fixings to the joists to prevent squeaking.'

http://www.londonbuildingcontrol.org.uk/news/?pid=3409&lsid=3422&edname=17824.htm&ped=17824

The idea is to minimise sound transmittance, in conjunction with mineral wool between the floor joists. In my experience, that's what a building inspector will look for.

 

[freddiemercurystwin]

Is this for a Building Regs Compliant Loft Conversion or just for storage?

 

[abuildingsite]

Is this for a Building Regs Compliant Loft Conversion or just for storage?

Good point- I assumed full loft conversion.

 

[softyengin]

whats this 15kg/m2 density thing?

i have a trusses loft, and i just want to store some things up there.
i was told in another thread that i can safely store upto 25kg/m2 thru-out the loft space.

another forum had a SE come in and told him for a similar roof type the limit was 5kg/m2.

I intend to weigh and spread stuff out, any idea which value would be safe to go by, 5kg/m2 is not very much!

cheers

 

[freddiemercurystwin]

Just stick some T&G 18mm chipboard up there and just be sensible with the storage, you people worry too much!

 

[softyengin]

brand new baby - just being careful!

 

[JohnD]

See how much you can get WBP ply for - it is stronger than chipboard, which is a terrible material. Some places will cut it to size.

The bigger the pieces you can get up there, the fewer joints you will have and the stronger and more rigid it will be. I can just carry an 8x2 sheet through my loft hatch.

 

[softyengin]

is WBP lighter? the lightest stuff possible would be best. as i can store more the lighter the 'floor' is

 

[JohnD]

I'm not sure. Someone will know, there are tables of densities of building materials somewhere.

If no reply here, ask on the "Wood / Woodwork / Carpentry" section //www.diynot.com/forums/viewforum.php?f=14

 

[ladylola]

the lightest stuff possible would be best. as i can store more the lighter the 'floor' is

You have to remember the impossed load of yourself as well as the storage. Simple test , put a piece of 12mm ply across two blocks and stand on it , or better still get someone else to stand on it and see how much it bends, then repeat with 18mm. As a comprimise form a pathway from the loft hatch in 18 or 21mm to stand and walk on with 12mm ply to the sides for storage. As you say it's only storage in the loft so it doesn't have to be pretty.

 

[softyengin]

i plan to have a row of the panels the full width of the house but under the eaves on each side.

so 30cm deep x width of house, should be fine for storing boxes and spreading load out across all the trusses at same time!

i will never be walking on them

 

[freddiemercurystwin]

FFS its a poxy bit of storage in his loft, all this rubbish about WBP is just a waste of money in this situation!

 

[Deluks]

Loft storage, whatever's cheapest!

Ply you'll get away with 9mm, osb 11mm, chipboard/mdf 15mm.
If you are storing so much weight that any of the above boards will become damaged from it then you have overloaded your loft joists.

LL 'test' isn't conclusive as the boards would (should) be screwed to the joists, reducing flex.

Unless you can get seconds/job lot/ebay bargain then what fred said, the 18mm chipboard t&g under a fiver a sheet, simples.

 

[softyengin]

i went to b&q to see whats on offer! less talk more action!

I found exterior plywood 12mm, i tried hard, struggled to bend it myself so thats seriously strong stuff!

i picked up the cheap £5.48 3-pack of chipboard flooring, wow that stuff is sooo heavy, forgot how heavy it was, although it is vastly cheaper.

im thinking i might go with the plywood option, but prob not from b&q, i guess they are the most expensive place.

its just so light and as im going to lay it across my new 'insulation raising joists' it will have a pretty short span so even less chance to flex. think im happy with this solution.

just need to find joist timbers now, current ones are 100mm by 35mm so prob get something similar.

cheers guys

edit, i'll see if i can find 9mm ply
edit2, damn that OSB is cheap need to check that out too!