Timber for Lintels

[Guss109]

You don't need steel, just timber of the correct size, it not only need to be large enough to carry the weight, but also carry the weight after being partially burnt in the event of a fire.

 

 

Hence why the steel plate is there. Every flitch beam I fitted when I was joinering was specced to have the steel plate. Guess it all depends on the local building regs ect

[Rob D]

I'm not sure on building regs but also bear in mind that the amount of movement you get in a large oak beam depends a lot of what tree it was cut from and the straightness of grain.

 

 

 

E.g you could cut a lovely looking straight beam from a bendy piece of wood - but this will have more movement than the same beam cut from a straight piece of oak.

[Chris Sheppard]

Hi Chris,

 

Oak has been used as a structural beam for a long long time.....don't worry about shrinkage etc there are ways of dealing with it...but it needs some thought...it also has to be the right bit of wood in terms of where it comes out of the log, grain flow, knots etc... Looking at your picture are your concrete lintels supporting the outer wall of the house or the concrete roof on the outbuilding ? I would carefully take some of those door opening header bricks out and see what room you have to play with before making any decisions on material. Have you enough room at the sides of the opening to properly support a lintel, just overlapping 4 inches or so onto a brick may not be enough....and may not satisfy any structural engineering requirements if their is a significant external load on the lintel.

Got any builder mates used to doing this kind of stuff, who can give advice ?

 

With the header bricks out we should be able to get 9" wide by 6" deep I think. Currently the concrete lintels are only on 4" overlap but we should be able to get a fair bit more on one end - the other might be a bit more difficult but worse case we could run another course of bricks up to get 8" overlap.

 

To get more than 4" at the other end of the wall we want out is doable if need be but am hoping we can get away with maybe 4" wide but quite deep piece going out that way. Maybe 9x9 for the piece to replace the concrete lintels and 8x4 for the piece to run where the wall is?

 

Sorry for the poor pic - the lintels are purely supporting the concrete roof - the photo was taken from the back door so everything in the photo is part of the outbuilding.

 

What I was hoping to do was to use a mortise and tenon joint to make up the T

 

Dad's been a civil engineer for the last 40 years and is retiring in about 5 weeks so will have plenty of time on his hands to help out - but his experiences with using wood in structural situations are a bit more limited

[Pete Bannister]

Chris,

Building Regs apply to everything There's no escape! I suggest the practical issue is this.. you dont want the roof slab to crack when you undermine it by removing existing support. If the existing slab is a pretty good concrete ( think you said its 6" thick) and if its reinforcement is beefy enough, in the right place in the slab, and in servicable condition, that slab may well span OK without the intermediate support. If your dad is a design engineer or if he's dealt with plenty of suspended slabs he'll be able to make an informed judgement about it simply be referring to span tables and having inspected the slab and perimeter support. The imposed loads from snow, wind and any access or storage loads must be considered as well as deadload. Any timber member (regardless of quality or species) would have to deflect before its providing support to the slab, you would do this by wedging between the timber beam and the slab. Shrinkage of timber could well be an issue and thats why timber is not the most sensible material to use, in this case. I spend much of my working life dealing with timber and specifying it as a building material.Timber is a fantastic building material; so is concrete, but the arrangement you are contemplating does not work to the best advantage of either. Thats not to say it wont or can't work!

good luck.

[agg221]

Chris, I'm not the specifier of mine, just the implementer! However from my position I agree with what Pete Bannister has said - which I think can be summarised as there are easier ways, but if you decide that this is what is right for you it can probably be done.

 

If you decide the aesthetics justify it then I would talk to a decent engineer - happy to pass on details of mine if you need them as he was very accommodating, e.g. it's easier for me to mill nothing bigger than 9"x9" so he designed the whole thing around this. He's also very good at knowing what's allowable as bearing length, what section you need for fire regs etc. You also need to take species into account in all the above - all the stuff I didn't want to find out! It cost us £500 for all the structural calcs for the foundations, walls, collar and purlin roof and removing the gable end wall and designing the replacement supporting structures, which I thought was good value for security of design and the ongoing point of reference for bits I don't understand as I go along.

 

You can definitely create 'T' shape load bearing beams, with flitch plates, as we discussed this at one point for ours. This was for using the stem of the T for halving the span of the joists and in the end we decided it was easier just to use 6"x3" joists.

 

It's worth noting that, although you want decent quality timber for structural reasons, hardwood is not subject to a certification scheme, unlike softwood, so you can use any decent timber you can get your hands on.

 

I have also found that if you work with Building Control they can be extremely helpful. If you work against them they get really official, which doesn't help in the long run.

 

Delabodge - no photos of my beam with flitch plate at the moment I'm afraid, as it's buried at the bottom of the pile of timber for installation, partly because it's one of the last pieces to fit as I stacked it all in reverse order to make it easier to get out when needed, and partly because it's too heavy to put anywhere else in the pile! As such, all you can see at the moment is the end of a beam with a slot in it. I'll take some photos once I've got it out, which will be somewhere in the autumn if the roof goes well and the rain holds off (ever).

 

Alec

[Chris Sheppard]

Thanks for all your replies gents, really helpful

 

I'm thinking maybe the simplest thing would be to go down the steelwork route. Keeps things simple and probably cheaper. It does seem like it would have been simpler to do using wood when building it in the first place rather than trying to make it fit after.

 

So, anyone had any good results hollowing out a beam to cover an RSJ?

 

Thinking if I'm going to end up boxing it in with plasterboard anyway, then it may as well get clad in something a bit nicer.

 

Pete, we're erring on the side of caution regarding the state of the concrete - it's been on 40 years and we can only see the underside of it as the top is covered. Reckon the smallish amount of extra work to include the intermediate will give a bit more peace of mind - on paper the span should be OK without it, but.....

[agg221]

Thanks for all your replies gents, really helpful

So, anyone had any good results hollowing out a beam to cover an RSJ?

 

Strangely enough, yes. I had a really complex interaction to manage between architect, listed buildings and the engineer. I had to get on with things during this period and that meant making parts to the then current design. At one point, the only way to span the upper opening was to use an RSJ, so I made a 'beam cover' U-channel to cover it. A re-design (by the engineer who worked out that the architect's drawing could be improved on) meant I didn't use it in the end, so it got cut down into three planks.

 

I made it from a green beam, milled it square, then cut a slot each side to leave 2" wide sides and a 2" thick base. I then hollowed it out with an adze. Worked fine.

 

Alec

[b101uk]

Steel, concrete and brick have the same expansion and contraction rates which is why they work so well together especially in the case of concrete and steel, or reinforced concrete wouldn’t work as it dose.

 

Would a wood beam not look a little crass in conjunction with a reinforced concrete roof?

[Pete Bannister]

with respect b101uk, they dont have similar expansion properties! That's why we use specific joint details when building with these materials.

I agree with your sentiment about concrete slabs and timber beams though.

 

Chris, you are right to er on the side of caution. BTW you can submit a Building Notice to your LA and pay a modest fee based on the value of the the building work you are doing. A building inspector is usually your friend in these situations. They are not designers but can often steer you in the right direction.

[b101uk]

with respect b101uk, they dont have similar expansion properties! That's why we use specific joint details when building with these materials.

I agree with your sentiment about concrete slabs and timber beams though.

 

With respect, stop and think for a moment vs. large structures made of reinforced concrete or wire/rod pre-stressed concrete, etc, etc, if it was the case of what you say it would be bloody stupid to put steel in concrete wouldn’t it if they were dissimilar in expansion and contraction property under normal temperatures