DIY Doctor UK DIY Forums

This is my first post- so hello! I'm building a large garage and need to know how to securely fix a wooden wallplate 100mm x 50mm onto the top of a wall made from lightweight aircrete 'superblocs' 150mm thickness. I'm concerned that any undue force or expansion of fixings would crack or split the blocks. Having seen some 'spiral' fixings that hammer through timber I'm wondering if this is the right direction or is there a 'usual' method that works - and which you are all going to tell me about?

Hi also a first post for me . just fix it with 4" nails from the top and you will have no bother :wink:

mmm. 4" nails? Do you mean cut nails - round wire nails - ring shank nails - galvanised? Fixed at what spacing centre to centre - skewed or straight in? I'm slightly doubtful as I've tried fixing batten to these blocks (aircrete) and found that they work loose with plain round wire nails, when hammering the next ones in.

Just standard 4" nails will do , your wall plate should be bedded on a cement mortar. The nails act as a tempory fixing for the instalation of trusses rafters etc to stop the plate from moving while installing these. you will then of course need to use special wall plate straps available from builders merchants that are then fixed to the wall plate and must then be scew fixed into the blockwork bellow to prevent the roof structure from lifting in the wind etc these are installed after the trusses in case you fit them in the position of one of the roof timbers, this is the usuall method used on buildings.
Sorry if it was unclear in my reply but it is only meant as a tempory fixing to allow roof construction.
The weight of the finnished roof will hold it in place it is upward lift caused by wind that causes the problems. the straps are around 1.2 m long with a 10 cm right angle at one end that goes over the plate.
Hope this helps.
Is your garage not subject to building regs ?

Perhaps I could have given more detail too. The roof is made from SIPs and therefore a clear span underneath without any roof structure except a ridge glulam beam where the panels meet. I will be straping the panels where they join the wall plate to the wall, at one metre spacing - so I see your reasoning about the need for just a temporary wall plate fixing. However, I think in my case this should be a stronger fixing still, as there will be more lateral (spreading) force on the wall plate than with a conventional triangulated truss. The garage is subject to Building Control, so maybe I'll ask for a visit. I have in mind to try long Fischer frame screws as these are classed as a heavy duty fixing according to 'Topbloc' who make the aircrete blocks.

I used to work for Durox Building products, and the most frequently asked question was regarding fixings, there are dedicated fixings for Aerated Concrete Blocks, Fischer have a nice selection. But a "standard" nail fix is a helifix- it's a twisted metal shaft and available in variuos lengths, screwfix sell them. Just to be sure you should use an exterior(solvent based) grip fill adhesive between the block and wall plate and glue the wood in place. PVA the top of the block to seal the surface. let it dry then apply the grip adhesive.