Load bearing timber between these supporting walls - will this work?

Hello everybody,

We're doing loft conversion in bungalow. I have two nearest supporting walls 502cm apart inner sides and 532cm apart outer sides. Our builder uses 30cmx5cm timbers for load bearing and the longest you can get is 520cm. So there'll be only (520-502)/2=9cm overlap between the timber and walls.

Is this long enough to work as load barer for the loft floor? Is there a building reg requiring a minimum overlap between load bearer and support wall?

Thank you

That is probably ok, its normal for the inner skin to be the load bearing one.

Assuming you are working off drawings and that timber is specified.

are you sure about the length? Normally softwood is 4.8m 5.1m, 5.4m 5.7m 6.0m etc

5.4m or 6.0 are common lengths -you would prob need to go to a timber merchant rather than builders merchants

It's hard wood (oak)
Just double checked - the length is 5.2m and it's the longest they make (Frank Key).

No we don't have architect drawings for the loft - I've drawn room layout myself in Smartdraw, but there is no load calculation from architect.
Building reg company is to check and approve everything before doing.

Then go to a saw mill who specialises in native hardwoods. Oak is available up to about 7.5 or 8 metres from saw mills, sometimes longer depending on the size of lorry they have available and the bed length of their band rack but is uncommon

Why do you need oak? Normally C16 or C24 graded structural softwood is sufficient in domestic builds and comes in long lengths more or less off the shelf. We are currently using C24 treated in sizes up to 20 x 12 on and that is available to us in lengths up to 6 metres providing we wait 3 weeks for delivery (because it comes in from Germany)

LikeMyHome said:

It's hard wood (oak)
Just double checked - the length is 5.2m and it's the longest they make (Frank Key).

No we don't have architect drawings for the loft - I've drawn room layout myself in Smartdraw, but there is no load calculation from architect.
Building reg company is to check and approve everything before doing.

Click to expand...

Ah ok

300 x 50 is a strange size in oak TBH, hence why I assumed it would be a softwood joist
I cant visualise why you would want an oak joist section.....

that is a big ask getting oak longer than 5.2m even that is pushing it.

12 x 2 (300 x 50) is the sort of size you see in ring beams. Never seen a joist that tall but so narrow - in older buildings they seem to go for wider and shallower on heavy joisting , (e.g 200 x 73 in C24 on my current project) although we did one job a few years back where the replacement joists had a 5.5 to 6 metre span and came in at 300 x 100 in 6.2 metres long lengths (C24). Those were bears to handle

Notch7 said:

Ah ok
I cant visualise why you would want an oak joist section.....

Click to expand...

This is not a joist - but large support timbers that runs doubled (or even trippled) in thickness along the edges of the roof (~400 to 800 mm away from edge). The floor joist are attached to them on joist hangers and run perpendicular to the timbers.

Why oak? Suppose due to hardness and longevity

JobAndKnock said:

Then go to a saw mill who specialises in native hardwoods. Oak is available up to about 7.5 or 8 metres from saw mills, sometimes longer depending on the size of lorry they have available and the bed length of their band rack but is uncommon

Click to expand...

We don't have stairs yet and feed thru old hatch in the ceiling - 4.8 feed thru fine, so 5.2 - should fit just aboutm but longer timber unlikely.

LikeMyHome said:

We don't have stairs yet and feed thru old hatch in the ceiling - 4.8 feed thru fine, so 5.2 - should fit just aboutm but longer timber unlikely.

Click to expand...

If we need to install big (long) stuff we either just remove a section of ceiling or roof to get it in and make good afterwards. This can be easier than having to put in two separate pieces with at least a 1 metre overlap (the minimum permissable).

LikeMyHome said:

Why oak? Suppose due to hardness and longevity

Click to expand...

That comes at a price, though, and not only high cost. Have you done the calculations on structural loading? The additional weight of oak as opposed to the far more commonly used softwoods may require larger padstones or even the use if corbels or pilasters to support it - and take a lot more physical effort to manhandle into position (ever installed large joists or beams?). Oak may not rot as quickly as softwoods in damp environments (with the obvious exception of softwoods like pitch pine which can outlast oak), but where inside any building which has been properly designed, constructed and maintained building is it ever going to be so wet that rot can kick off? I've done a lot of work on larger listed buildings (mostly 100 to 250 years old) in recent years and rot in beams is invariably down to poor gutter and roof maintenance, allowing water to leak into the building. One other thing that is certain is that some pitch/resin-rich softwoods such pitch pine are actually better at resisting beetle larvae attack (ever heard of that destroyer of old oak beams, death watch beetle?).

So other than possibly snobbery, unless the timber is on show, I can see no reason why a C24 structural softwood beam wouldn't be a better choice (and if you are using oak timber in a structural setting it is a requirement under the building regs that it has been structurally graded - most timber yard oak isn't)

I apologies I' ve mistaken and misguided you - our timber is not oak, it's a soft wood (attahed). Probably pine.

JobAndKnock, thanks a lot for your explanations wrt timber rot etc - very helpful indeed!

JobAndKnock said:

If we need to install big (long) stuff we either just remove a section of ceiling or roof to get it in and make good afterwards. This can be easier than having to put in two separate pieces with at least a 1 metre overlap (the minimum permissable).

Click to expand...

That's how our builder proposed to do this - but so far we've been ok feeding up to 4.8m thru the loft hatch and 5.2m that we ordered recently should hopefully fit as well, thanks