Oak beams

[trevorbayliss]

I am using some big oak beams in the roof of my new extension.

There will be 4 structural beams holding up the flattish roof. On top of these beams will run my 125mm rafters. Then insulation on top and ply sheets and then a metal roof finish.

My question is how i attach the rafters to the oak beams.

I was thinking about using a nail plate at 4 points down the rafter. So i would be nailing into the rafter and the oak beam. I would use sheridised twisted nails as well.

Do you know if nailing into the oak beams is doable ? I have read these beams need to be drilled for most things and are very hard.

I am not using green oak, but seasoned 3-5 yrs.

 

[bernardgreen]

Do you know if nailing into the oak beams is doable

It is "doable" but you have to consider the corrosive effect that oak has on metal. Wooden pegs will last longer than most metal fixings

 

[trevorbayliss]

But I cannot use pegs to secure the rafters to the oak. So it has to be a stainless metal.

Do you know if Sheridised nails are ok?

 

[bernardgreen]

Some grades of stainless steel can be used in oak. I cannot recall which grade(s) can be used in oak without being corroded.

If the rafters are lying on top of the beams with no lifting force then this method of fixing might be acceptable. The blue pieces can be sculpted into a more ornate shape

 

[Notch7]

your oak will be wet inside so steel with sheradised or zinc coatings are likely to rust, although the oak is in a dry environment so its MC will go down over time and there is no risk of rainwater. Maybe you could use the higher resistant coated screws like decking screws.

Stainless steel is an obvious solution, which will still probably stain but wont rust. However you would have to be vigilant and pilot every hole, with a fair size drill, not much less than the screw diameter, or you will suffer with snapped screws.

 

[trevorbayliss]

Thanks for the info Notch.

This seems a better solution than using pegs described by bernard. The pegs would be a nice solution if i had the time, but i think these will take to long to create and drill etc.

So i need stainless screws. OR stainless nails would be even better perhaps. Do they make them?

I was hoping to use nail plates like these

https://www.toolstation.com/shop/Co...alwork/sd2797/Nail+Plate+Angle+Bracket/p91000

 

[trevorbayliss]

Another possible method is to drill one hole from the top of the joist down and into the oak purlin. I would then screw down with a hex flanged hard screw. I remember speaking to a joiner about this and he suggested doing this.

I have 5 oak beams and probably 20 odd joists to screw down, so thats 100 screws needed.

This would be more cost effective i think than buying the nail plates and nails or screws.

My joist is going to be 125mm, so the screws need to be 150mm minimum i think. I would try and screw them down into the joist by an extra 25mm as well. So in the oak by 50mm.

What do you think to this method ?

 

[Notch7]

Yes, if you have access above, drill through joist and screw through.

I doubt if you woukd be able to pre drill, so use decent screws or hex bolt screws.

You wont get them in stainless, but does that matter?

150mm or 160mm screws. Or 120 mm screws and counterbore, although that would be more work for no need.

 

[trevorbayliss]

Ok i think this is the best option. I will see if i can get a long drill bit to pre drill. Sounds like it might be needed.

I will need to bore out a little i think for the screw head anyway. Not used these screws before so cant say for sure.

 

[Notch7]

Something like these....

https://www.screwfix.com/p/fastenma...ersunk-screws-black-6-3-x-150mm-12-pack/70785