Calculating size of oak beam lintel?

[Lauraalgar]

Hi all,

Hoping to replace an old oak lintel as we discovered an original fireplace behind a newer brick facade. Was going to replace with an air or kiln dried piece to fit the existing hole, but concerned it wouldn’t be enough to take the weight (hole would allow for a 4x4 inch ish beam - and I’d have it spanning the entire width of the breast).

Might anyone be able give any guidance/have any experience of doing this? Have tried writing to a few structural engineers but no reply after two weeks and it’s looking rather precarious (though it’s been standing behind the facade since the 70s or so) - keen to get something in asap…

Quite happy getting it in with some strongboys, and remortaring the brickwork above too, just the sizing of the beam I’m not sure about…

Pic attached for ref.

L

 

[noseall]

Hi all,

Hoping to replace an old oak lintel as we discovered an original fireplace behind a newer brick facade. Was going to replace with an air or kiln dried piece to fit the existing hole, but concerned it wouldn’t be enough to take the weight (hole would allow for a 4x4 inch ish beam - and I’d have it spanning the entire width of the breast).

Might anyone be able give any guidance/have any experience of doing this? Have tried writing to a few structural engineers but no reply after two weeks and it’s looking rather precarious (though it’s been standing behind the facade since the 70s or so) - keen to get something in asap…

Quite happy getting it in with some strongboys, and remortaring the brickwork above too, just the sizing of the beam I’m not sure about…

Pic attached for ref.

L

View attachment 322574View attachment 322577View attachment 322578

Will the beam not contravene the minimum heat distance rules/regulations?

 

[Lauraalgar]

Will the beam not contravene the minimum heat distance rules/regulations?

We’re replacing the old stove next year and the chap has shared several ways to manage the issue to satisfy regs, so that side of things is fine (emailed him before settling on wood vs steel/concrete) - thanks for checking!

 

[noseall]

Hi all,

Hoping to replace an old oak lintel as we discovered an original fireplace behind a newer brick facade. Was going to replace with an air or kiln dried piece to fit the existing hole, but concerned it wouldn’t be enough to take the weight (hole would allow for a 4x4 inch ish beam - and I’d have it spanning the entire width of the breast).

Might anyone be able give any guidance/have any experience of doing this? Have tried writing to a few structural engineers but no reply after two weeks and it’s looking rather precarious (though it’s been standing behind the facade since the 70s or so) - keen to get something in asap…

Quite happy getting it in with some strongboys, and remortaring the brickwork above too, just the sizing of the beam I’m not sure about…

Pic attached for ref.

L

View attachment 322574View attachment 322577View attachment 322578

We'd fit a steel lintel above then fit a décor oak beam.

 

[^woody^]

And remember, oak will shrink considerably months later as it acclimatises

 

[Notch7]

I can’t see a 4” oak beam being strong enough at all.

I reckon you need a steel in there - like a chunky angle or something.

 

[Dereekoo]

Well in theory and assuming there aren't any other loads acting the on the wall from behind the ceiling beams i.e. floor joists, then the only load that needs to allowed for is the triangular brick section above the lintel due to the brickwork corbelling most of the wall load to the side. This can be seen by the actual lines of the failing brickwork above the existing brick lintel. Estimating a span of 2.15 and for the sake of simplicity of design assume that the the lines run up at 45 degrees which would mean a maximum triangular load of a half brick wall acting on the span of 2.15 x 0.5 x 2.15 x 0.5 x 2 x 0.1 x24 = 2.8kn. This gives a maximum bending moment of 1knm, using C24 permissible stresses as used by TRADA for joist sizes (Oak is actually stronger) then a 100 x 100 lintel would be able to take a load of 1.4knm whilst having a 6mm deflection which is just on the permissible limit for flooring etc but whether it would be aesthetically acceptable for your fire place??

 

[Notch7]

You might find an oak beam at a reclamation yard, it will cost a fair bit more as you prob need to buy a long length and cut out the bit you need - but it would be very well seasoned.

If buying new, avoid green oak like the plague, get air seasoned stock which will still shrink but not do much.

Try and get straightish grain as that will minimise twisting, bowing etc

 

[Dereekoo]

And remember, oak will shrink considerably months later as it acclimatises

Surely that depends on the initial moisture content and if its been kiln dried?

 

[noseall]

Surely that depends on the initial moisture content and if its been kiln dried?

It's rare to see zero shrinkage, on any timber beam. Trouble is, with the best will in the world, the beam takes on moisture whilst it's being built in. It then shrinks away from the masonry and plaster.

 

[Lauraalgar]

Thanks all, and thanks @Dereekoo for taking the time to share your calcs, I knew that’s what I needed but was struggling to work it out - clear span is 145cm so your suggested load is ample. However I think after some circling conversations with the hubs that we’ll relent and go for a reinforced cement lintel for ease and piece of mind as it really needs to put in. I’m lime plastering the breast so I’ll just plaster over the lintel and look to hang a wooden beam or something similar afterwards.

Thanks as always for your time!

L

 

[bsr]

How about a 100x65 PCC lintel vertically into the space with a 100x50 oak beam in front?

Or a 100 X 60 box section:

Rectangular Steel Box Section (S235) | 100 x 60 x 6 | RHS

RHS (Rectangular Hollow Section) in 100mm x 60mm x 6mm, and in steel grade S235, for use in rails, gates and more steelwork projects.

shop.buyabeam.com