Timber for Lintels

[Chris Sheppard]

Not sure if this is in the right place so bear with me

 

On the side of our house is a single storey, brick out building with a 6" poured reinforced concrete roof, that once upon time was probably an outside toilet and coal shed (two separate rooms). but at some point had a roof put between that and the house and a door on each end and became a bit of an extension to the house.

 

What we're planning on doing is knocking the dividing wall out to make the outbuilding into one bigger room - some of the neighbours have done the same but either risked not using a lintel or used steel.

 

I've no problem with doing it with Steel, but I'd prefer to do it out of timber (partly for aesthetics and partly as it won't hold the cold as much), especially as there's relatively little weight to support and only over a relatively small span (sub 6ft).

 

However, I've never used wood in an application like this and wondered how you get round any movement in the wood compared to steel which should pretty much be inert - I'm guessing we'd have to use something that was suitably dried already, but are certain species better/worse than others? Might have enough bits of Oak to do it out of but would take some drying out, but not averse to using some shop bought kilned softwood if I had too.

 

Also do you still put a fillet of mortar on top like you would with steel or just push it up into place and fill below it?

 

Hope that makes more sense that it did to me reading it back

[skyhuck]

Dead Elm is good because its so dry, very little movement if any.

[Guss109]

What you are thinking of is called a flitch beam/plate. It's just a steel plate sandwiched between two bits of wood

[skyhuck]

What you are thinking of is called a flitch beam/plate. It's just a steel plate sandwiched between two bits of wood

 

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.

[agg221]

Only down-side to elm is that it is very prone to severe woodworm attack. If you can find some without it, great, then treat it heavily to stop later attack.

 

Timber dries at about an inch thickness every six months, so a beam takes a long time to air-dry. Most of the time the thing you're supporting has a certain amount of give - a tiled roof can flex a bit, as can floors, ceilings etc. If you have a poured concrete roof that isn't going to like it, so I'd be concerned about the effects of any movement.

 

How big are you thinking of going? You could do what was specified for my first-floor beam where I'm knocking out the gable end wall of the house. I'm using a 9"x9" beam but it has a steel plate (flitch plate) let into it. I cut a slot from the top, going about 7" in, using a chainsaw, controlling depth and straightness using bits from the Alaskan (if i had a mini-mill this would have been even easier). This accelerated seasoning a bit - in yours I'd be looking to use something dry anyway. I then dropped a piece of 10mm steel plate in to the slot, which is bolted through every couple of feet. You could do this and plug it to disguise the bolts but I'm using square nuts and washers and painting them black. If you did this and made the plate full depth at the bearing ends (where it won't show) this would control the depth absolutely with the steel, so it wouldn't risk movement, and would give you the aesthetics and reasonably restrict thermal bridging?

 

Alec

[delabodge]

Only down-side to elm is that it is very prone to severe woodworm attack. If you can find some without it, great, then treat it heavily to stop later attack.

 

Timber dries at about an inch thickness every six months, so a beam takes a long time to air-dry. Most of the time the thing you're supporting has a certain amount of give - a tiled roof can flex a bit, as can floors, ceilings etc. If you have a poured concrete roof that isn't going to like it, so I'd be concerned about the effects of any movement.

 

How big are you thinking of going? You could do what was specified for my first-floor beam where I'm knocking out the gable end wall of the house. I'm using a 9"x9" beam but it has a steel plate (flitch plate) let into it. I cut a slot from the top, going about 7" in, using a chainsaw, controlling depth and straightness using bits from the Alaskan (if i had a mini-mill this would have been even easier). This accelerated seasoning a bit - in yours I'd be looking to use something dry anyway. I then dropped a piece of 10mm steel plate in to the slot, which is bolted through every couple of feet. You could do this and plug it to disguise the bolts but I'm using square nuts and washers and painting them black. If you did this and made the plate full depth at the bearing ends (where it won't show) this would control the depth absolutely with the steel, so it wouldn't risk movement, and would give you the aesthetics and reasonably restrict thermal bridging?

 

Alec

 

got any pics of that alec? fitch plate,,,?like to see it,,,

[Chris Sheppard]

Thanks for the replies guys.

 

Hadn't thought about what would happen in the event of a fire - that's a good point Dave

 

A Fitch plate sounds like it would make things a lot easier, I'm liking that idea

 

Does the timber that's encasing the steel help to stiffen up the steel or is it purely cosmetic?

 

Where the original doorframes are, there are two 4"x6" concrete lintels that join in the middle where the dividing wall is, with taking out a bit of cosmetic brickwork we could fit a 6" deep by 9" wide timber in. Going out along where the dividing wall is coming out is currently only single brick thick so might need to make the pillar at the far end wider yet, but as it is could take 4" wide and 6" deep.

 

I'll try and get some photos today to show it better.

[Pete Bannister]

Chris,

photos and or drawing would help. The timber pieces in a flitch provide resistance to torsional forces that develop as the steel or iron plate deflects. A flitch beam is an overly complicated and expensive way of providing a lintel unless there's an important aesthetic involved. It is more often than not more important to protect structural steel from fire than it is to protect timber (which, when of sufficient section, self-protects for a time). Structural timbers need to be fit for purpose, mechanically and provide adequate durability. You cant use green timber to support brittle masonry structures without problems as movement occurs through drying.

In general terms what you are proposing very probably involves 'The Building Regulations'. Its you statutory obligation to comply. This isnt necessarily a big deal..but you should be aware of a few issues. It may well be easier and cheaper in the final analysis to use a proprietary concrete or steel lintel.

[Chris Sheppard]

I'm hoping that as it's only an outbuilding and not officially part of the house as such, that we might be OK keeping it unofficial

 

Hope photo shows it a bit more clearly - I can't get far enough back to get any more in.

 

If we have to go down the official route then I think it might have to be steel as we need to put it in as a "T" - the top of the T going between where the doorframes were and the long bit of the T going back towards the back wall.

[aswales]

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 ?