Anchoring an oak frame - advice please

[AJB Temple]

Advice would be appreciated on whether and how to anchor a green oak frame to a dwarf wall. I am building two small barns for use as outbuildings, about 6m by 6m. Reinforced concrete slab is in and fully cured. It has a yet to be built brick perimeter dwarf wall on three sides , 9" thick and three, possibly four courses deep, incorporating DPC. Posts set on granite staddles with rebar anchors above (not below). One of the barns will be open at the front. The other will have doors. Neither opening faces the typical prevailing wind. Roof will be clay tiles, so significant building weight as entire frame, rafters etc are oak.

The oak plate laid on the 9" dwarf wall is 175mm square green oak. What steps would you guys take to anchor the oak frame to the dwarf walls. I do not want to see anchor straps. I have not laid the bricks yet so I can drill the concrete easily enough and build bricks around fixings. Tapcon or similar springs to mind but should I just stick some steel rod in and hide it in the oak with pegs?

I have quite often seen green oak buildings erected on dwarf walls without any fixing to prevent lateral movement, but I am not sure whether this is smart.

(The last time I did a barn was 20 years ago and I can't remember what we did then as i employed a builder to do some of work and was not there when the plate went in. He's dead now.

AJ

 

[MikeJhn]

Don't anchor the green oak to the brick wall, if you feel the need a slotted hole in the oak with a vertical pin in the wall will allow some lateral movement which is inevitable with the different co-efficient of expansion of these two interfaced materials, the overall weight of the barn will keep it in place, its just expansion that needs addressing, fixing the Oak to the walls will lead to cracking of the walls.

To reinforce the above the Tudors knew a thing or two about timber construction and did not use any connections between the dwarf walls and the Oak wall plates, the wall plates where just sat on the wall and joined together at the corners.

Mike

 

[AJB Temple]

Thanks Mike. That was my original plan, but then got agitated about wind pressure. Adrian

 

[Peter Sefton]

When we did our barn conversion we drilled and resin bonded 16mm stainless steel bar into the slab and built the brick work around them, the sole plate is bolted down prior to the rest of the construction. Still leaving in the barn 8 years on with no problems.

Cheers Peter

 

[Woody2Shoes]

I've been making a porch (green oak, sitting un-anchored on top of masonry walls) which was moved by the wind while battened and felted, but before it was tiled - I've now anchored it with hidden steel brackets!

Based on my own experience, I would use bits of stainless studding as vertical pegs between masonry and timber held into the masonry with resin as already mentioned - only one or two for each plate - with an allowance for timber movement.

Certainly, building regs normally require quite significant steel straps between timber wall plate and masonry wall in habitable spaces e.g. http://www.strongtie.co.uk/products/det ... -strap/333

Cheers, W2S

 

[Peter Sefton]

Timber movement shouldn't really be an issue as timber doesn't shrink in it's length.

Cheers Peter

 

[Woody2Shoes]

Timber movement shouldn't really be an issue as timber doesn't shrink in it's length.

Cheers Peter

The thing I've found with green oak is that it can quite often twist, and, less often, bow a bit along its length as it dries out - the pieces I've used generally aren't centre-free (which often causes checking and/or uneven movement across the width) and always have knots etc. If it's a tug-of-war between oak and masonry, oak will nearly always win, so I err on the side of caution! Cheers, W2S

 

[AJB Temple]

It is wind pressure on the building that is my concern. The green oak is bound to move to some extent. It is high quality QP1 but green is green!

 

[Wuffles]

When I built my porch, I drilled and screwed into the dwarf wall, then plugged the holes. You'd be hard pushed to see them. I used the fixings that I used for the green oak sleepers on the patio.

 

[Peter Sefton]

Green oak will always move whilst drying over a matter of years and it's very hard to stop it but having a buildings weight on it will help.

Cheers Peter

 

[MikeJhn]

This document will give you an insight into the wind loads applied to your building: http://www.mcrma.co.uk/pdf/Wind_guidanc ... _final.pdf To be accurate a site assessment needs to be carried out to establish the exact loads that will apply.

None of this information was available in Tudor times and they relied on the mass of the building to keep it in place, but then they used much larger timbers and where not scared of using up resources, in these modern times we use much smaller mass/lighter timbers due to cost constraints and availability.

Mike

 

[Phil Pascoe]

Just a word of warning (if this hasn't come up in one of your posts before) - don't be tempted to mix galvanised fittings with stainless ones (with any wood not just oak, but you're likely to be using stainless with oak). Sometimes it's hard to get hold of the right sized washers in stainless. The reaction between the different metals will cause the galvanise to come off and they will rust.