Flitch Beams

[Shane Davis]

We are undertaking the build of a new extension to our grade ii listed cottage and where possible, we are trying to use reclaimed materials to retain the period features present in the existing house. In two areas the architect and/ or technical engineer has specified flitch beams. Is there any way to create a "period" looking beam and still hide the steel without using a box method?

 

[Penners]

I'm no expert, but I believe a flitch beam is a kind of wood-steel-wood sandwich, isn't it (sitting on its edge)? Could the wood be green oak? if so, then all it would take is a piece of oak patched across the soffit of the beam for it to be a fairly aesthetically acceptable in a period house.

I can't think of any other way of doing it.

However, I'm interested why your architect has specified this kind of beam in a grade II building. Could the job not be done with a solid oak beam, appropriately specified?

 

[biffvernon]

OED:

flitch n Side of pork salted or cured.
flitch-beam. compound beam, esp. of iron plate between two slabs of wood

I don't know what they teach them at Architectural school these days but there does seem to be an aversion to using timber beams when you could use a more expensive steel one that will fail in a fire. I would tell your architect "No, I'm having oak beams. Just look up the required dimensions please and then double it so it doesn't look mean." You should be paying about £15 per cubic foot for a new oak beam.

 

[MJ]

I wish I had Biff's advice when doing work on our place. Stand your ground and say you want Oak beams.

As Biff says they are better all round.

 

[middi]

I heard on the grapevine that architects and structural engineers are very reluctant to use oak beams in new build especially in a " mix and match" situation as ( apparently ? ) there is not a standard stress calculation procedure which they can follow.

It stands the reason why in a run of the mill, bog standard, conform to regs and so on applications, will throw the spanner in the works as far as calculations go.

Tell them to use a nice overengineered massive beam, this will solve all the problems . It is proven science without calculations.

 

[Nigel Watts]

The alternative is to use modern materials and allow them to speak for themselves. The worst option, I would suggest, is to use modern materials faked up to look like something they are not.

Blending old and new effectively is not always easy to pull off but in some ways it can be more satisfying than trying to match old work; it does not confuse anyone as to the extent or nature of the orginal structure, it is arguably more honest (William Morris I think would agree on this point), and modern design can be very pleasing when done well.

In the modest side and rear extensions to my Grade II 1840 townhouse I used steel and glass and fitted out the new spaces in an entirely modern style. The old rooms however I am restoring and decorating in something much closer to an early Victorian style.

 

[biffvernon]

As Biff says they are better all round.

Hmmm, I've a friend in France who used round beams because it saved milling the tree but square beams are more common.

Couldn't agree more, Nigel. If you are going to use steels then leave them exposed. They can look great in the right context.

 

[nickO]

According to my Bible , Brunskill's Timber Building in Britain a flitched beam is " a type of beam made by taking a balk of timber , sawing it in half,turning the two halves back to back to reveal the heartwood , inserting a steel or wrought-iron plate between the two pieces and then bolting the three together.Such a beam was stronger than the original balk . "
Basically what the others have said .
What is the length of the span , and what is it supporting ?

From an unqualified , but practical, builder's point of view the use of a flitched beam is a load of nonsense . Just whack a big lump of oak in there . There are so many examples of this practice working perfectly satisfactorily that I can't even begin to see why this is an issue .

Just another case of an architect trying to justify his fee .

 

[Johneds]

A flitch beam is a solution that would be measurable, safe, reasonably easy to produce and probably the cheapest option. I don't think any architect would object to a solid oak beam but a beam of the right proportions and length might not be easy to find and when you find it you will need a structural engineer to confirm that it is safe. In order to confirm this the engineer might have to have the beam stress graded. None of this is impossible but it will certainly cost a lot more than a flitch beam.

 

[biffvernon]

I bought some 6 inch square English oak recently. Straight grain, no knots, no splits. I'm no structural engineer but I reckon they'd hold up a modest cathedral for a few centuries. Cost: £15 per cubic foot so that's £3.75 per linear foot (+VAT). I think flitch ought to be kept for bacon.

 

[Penners]

I sincerely hope you'll have it stress graded and carry out a Risk Assessment before you do anything as rash is building with it, Biff.

 

[Me!]

Biff, are those prices for green oak or seasoned?
Also, I believe it takes a year per inch of thickness to air dry oak, but presumably this can't be a linear one inch per year up to any thickness? And if a 6" square section was kiln dried wouldn't it just split badly?

 

[Penners]

For structural use, oak is often used "green", rather than kiln or even air dried. It will progressively shrink and often crack in situ, but its huge strength (and usually the degree of overspecification) makes these cracks totally unimportant. Look in most old oak frame houses and you'll see cracks in many of the beams - particularly the large section ones like king joists.

 

[biffvernon]

The 6 inch square was green - such thicknesses don't really dry out in any reasonable time. When I buy boards for joinery I get air dried. It's been stacked for 2-4 years depending on thinckness. I don't use kiln dried.

 

[Penners]

Bit of a b*gger if you want to do a quick repair on the bedroom floor, though!

Still - there's always those nice click-together "genuine wood effect" laminates from B*Q. :x

 

[biffvernon]

My nice saw mill has done the stacking first. That's why 3inch thick boards cost more than 1inch - you pay to have had it cluttering the yard for years.