Lengthening beam

[TimD]

I currently have a single story extension to my house that is part of the original building which is over 100 years old. This is now used as a kitchen and the back quarter is of single brick construction. A previous owner has removed part of the wall between the two parts and put an rsj in place. Unfortunately the beam is only about about half the width of the room.

I intend to build a cavity wall internally to the single skinned part and would also like to put a larger beam across so that I can a nice rectangular room in which to fit a new kitchen.

Existing

xxxxxxxxxxxx x x Flat roof x x xxx------xxx location of old beam xx xx xx xx xx xx sloping tiled roof xxxxxxxxxxxx xxxxxxxxxxxx

Planned

xxxxxxxxxxxx xxxxxxxxxxxx xx xx xx--------xx location of new beam xx xx xx xx xx xx xxxxxxxxxxxx xxxxxxxxxxxx

I have been advised by a builder that as the building is single story and the beam is only supporting a roof above that there is no need for an rsj, but instead a flitch beam could be used, which could be cheaper and easier to install. I would welcome any advice from the group on making and installing a beam, as well as suggestions on where to buy the steel, bolts etc. I want to get some sort of comparitive costs before taking this further.

Thanks Tim

[John Rumm]

As an aside, unless you have another reason to add the inner skin, you could simply insulate the wall inside and then dry line and skim it to bring it flush with the thicker wall.

What length will the new beam need to be? It may be you don't even need a flitch.

They are simpler to install in the sense that they can be assembled close to where you need them - which can be a big deal if you need to get them up ladders etc. Probably less of an issue for you in this case. You may even find you can assemble it in situ. The advantage here is you only need to lift a third of the weight into place at a time.

A flitch is just a steel plate sandwich with a couple of wood beams for "bread". They are usually bolted together with 12mm thick bolts with plate washers either side of the wood. Typical spacing is 50mm in from the edge, 600mm apart, on alternate sides.

You will need to find yourself a local steel supplier - if you don't know of one, then phoning a local builders merchant should get you a suggestion. Said BM will probably be able to tell you the cost of the wood (although something up to a couple of quid per linear meter for

8x2" would be a good estimate). The steel and bolts etc. for one flitch is likely to be under 50 quid + delivery. If you tell the supplier what it is for they will usually pre drill it and paint it with a passivating paint as well. You can then use it with a 12mm auger bit as a template for drilling the wood.

[Christian McArdle]

It all sounds pretty cheap and easy for a builder to do. Also, if you know a friendly structural engineer, they may be able to suggest an ever cheaper solution. If the best case, you might find you just need a couple of tie rods to prevent the walls spreading.

Christian.

[Jerry Built]

I doubt it, sounds like a lot of ubggreing about, to me. I should see about a steel beam first.... how long does this need to be?

J.B.

[IMM]

Steel? Expensive and over engineered to support a small part of a roof.

[Jerry Built]

Not very expensive, not very heavy, lots less fiddling about and wasted time and bugging about than making up a flitch beam.

J.B.

[Tony Bryer]

How can the right size of steel be "over engineered"? A steel beam might well be the most appropriate choice particularly if headroom is a consideration.

[TimD]

I have just got a price of £120 for a 178x102 beam of 3.6m long. A Flitch beam (not including wood or screws, but pre drilled) was £160. So no contest really. I don't think it is going to be that tricky to install a beam weighing less than 70kgs.

Also got a quote for a structural engineer to come and look and he wants £300 + VAT. This seems very expensive, is it any wonder that there are so many posts in this forum from people who are trying to avoid using their services.

I have tried out the demo version of Superbeam, which seems very easy to use. I have put a total load of 1.5 kn/m2 which is the standard live + dead load for a tiled roof. I have also put in an effective length of x 1.1 (to account for how the beam will sit on the wall, and it still comes up with a recommended beam size of 127x76mm. Hopefully Building control will approve my considerably overspecified 178x102! Have I missed anything? I certainly don't intend paying an engineer £360 for less than 30 minutes work.