How to install a Flitch beam, advice please

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Hi please could somebody guide me through the next part of a job I’m doing in my house. I got some advice from a builder friend but his company have sent him to a job in a different area for a month or 2 and I want to get on.

Basically I live in a cavity wall 1930’s semi house in which I have removed the chimney breast in our bedroom on the 1st floor in the past and I had a builder cap off the top part first with gallows. So now after having a builder check what I need to do, I removed the ground floor chimney breast and I have cut the slot for the lintel and new beam.

Room is 4.3m x 3.3m, he said the walls between our houses are probably 9” but could be 13” but to go with 9” for the purposes of this job.
When they built these houses, they ran the joists in the 1st floor/ground floor ceiling, along the longest room length so instead of towards the chimney breast (3.3m) they ran them across the room (4.5m)

Because they did this they ran 2x 6” x”2 butted up to each other across the joists to support them and into the chimney breast a few inches. My builder said this was a little unusual and this beam was just to take the spring out of the joists due to their length and that it would all stay up without it but might be too springy. Although it may all be alright without it he advised to support whilst removing the chimney and fit a flitch beam in its place and rest this on a 300mm lintel. He said just buy a 600mm lintel and cut it in half. He said order a Flitch beam 150mm x 10mm x room length +allowance for resting in wall at each end and that would give me something even stronger than what was there before.

I did not know what a flitch beam was before this job but he explained and I read up on the net too. So as I understand it, I order the Flitch beam with holes predrilled for me and bolt two new 6” x 2” timber beams the same length as the steel to it. He recommended holes every 6” which seems excessive to me and after reading on net it seems you ask for them to be not along the middle but rather 2” from the edge at alternating edges and not more than 600mm apart maximum. So if 600mm is maximum what should I go for in this job?

Also reading on the net it advises against cutting lintels as they are pre-stressed but there is a lot of arguments either way.

So now my questions, sorry I go into too much depth and worry too much about detail but it’s because I have not done this before.

So can someone on here confirm should I have holes every 6” on the Flitch beam 2” away from alternating edges or what do you suggest?

I want to cover the flitch beam in Oak so is it ok to drill holes big enough in the timber to accommodate the nuts and washers i.e. to recess them or will that weaken it or am I supposed to let them protrude, in which case how would you mount the Oak cladding?

What size stud do you think I should use for the Flitch beam, my builder recommended 10mm studs, does that sound ok?

The place you go to get the Flitch beam, can they make it up for you, i.e. fit the timber to it, or is that something you normally do yourself, I assume if they did it, it would work out expensive?

Since this beam is only to stop the joist flexing and not major support am I worrying too much about stuff and should I just accept that this beam will be more than enough?

Will it be ok to cut a 600mm lintel in half and use it like that again because this is just to take the flexing out of the joists, or should I be concerned about this and not cut it, in which case what should I do as 600mm seems a lot of unnecessary cutting out for this job?

When I put the Lintel in do I cement it in place first or do I get the whole lot up and beam in place and cement with everything pressed up against the ceiling?

What mix of sand and cement do I use to cement the lintel in considering it is supporting?

I would love any answers to my questions confirming my methods or telling what else I need to know.

Sorry I’ve gone into so much detail on what is probably a simple job to a builder, but any help appreciated.
 
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/following may not be helpful.

Normally designed by an engineer.

Somebody nice might advise you based on what they normally do, and it might work, my advice is get someone to design it properly.

Might also help to just state the clear span, and dimensions of the timber you desire in one clear line, rather than having to hunt for it through a big post.
 
Flitch beams are useful but they rely on the composite action between the steel plate and the timber members. There are a number of ways to produce them. All of them need to be designed by a Structural Engineer. You will also need to Building Regs approval.

To answer your specific questons:

I am not sure what you mean by "Covering the flitch beam in oak". A flitch beam is formed from the oak and the steel plate.

The holes in the timber need to be a tight fit for the bolts in order to achieve the composite action.

If you use a wider oak beam, you could countersink the bolts and then plug them.

Cutting prestressed concrete lintels in half is OK. Not sure why you need one only 300mm long though!
 
Flitch beams are useful but they rely on the composite action between the steel plate and the timber members. There are a number of ways to produce them. All of them need to be designed by a Structural Engineer. You will also need to Building Regs approval.

To answer your specific questons:

I am not sure what you mean by "Covering the flitch beam in oak". A flitch beam is formed from the oak and the steel plate.

The holes in the timber need to be a tight fit for the bolts in order to achieve the composite action.

If you use a wider oak beam, you could countersink the bolts and then plug them.

Cutting prestressed concrete lintels in half is OK. Not sure why you need one only 300mm long though!




I'm trying to avoid the cost of the Structural Engineer for this job as my builder told me this work is fairly minor, as this is only a beam to stop any flexing in the joists, and not a major support.

I have removed 2 x 6"x2" and will in effect put them back but 8"or so longer (so 2 new ones) but this time including a 10mm plate, so after what my builder told me too I don't see it really requires me to make such a massive job out of this. Yes this is not my exact field although my background is in engineering, but I feel fairly confident after seeking builders advice that I can do this, I just need to clarify some points as I would like to do the best job I can possibly hope for.

I am surprised at what you say about making the Flitch beam out of Oak and steel plate as I have asked on other sites too and no one says that a Flitch beam needs to be constructed from Oak, I want to cover it in Oak afterwards to make it look like an Oak beam.

Thanks for the tip about the tight holes, I will make them so they are as tight as is possible to still get the studs through. If I use 12mm stud would I drill the timber holes at 12mm or less and what holes would I ask for in the steel?

I am thinking the construction of the Flitch beam will be so big and so be not sensible to try and cut out the necessary void in an Oak beam to cover it and so cladding seems the only way to achieve the Oak beam look in this case, unless you can suggest a different way?

I need 2x 300mm Lintels, that's why I am saying to buy a 600mm which seems the shortest readily available size and then to use one 300mm at each end of the beam. Incidentally the existing beam just rested on the brick so this should increase the beams performance/strength I feel.
 
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A flitch beam needs to be properly designed like any other structural support. Why are you using 10mm plate and 12mm bolts?
 
For goodness sake, why faff about with a flitched beam?

If I read you correctly, you are putting this beam under the centre of the floor, spanning long-ways, to take the spring out of the existing floor joists?

Then use a 152 x 152 x 30 steel beam, 'Fireline' it, and then clad it in an oak finish.

Making up a flitched beam would probably be more expensive and time-consuming.
 

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