Installing lintel above window

[alexanderbourke@hotm]

Hi All

I've kind of hit a brick wall, no pun intended.

My builder is ready to install a window in a timber frame domestic dwelling on the ground floor, with no windows or opening above. The windows span is 1200mm and I have provided the council with the details of the lintel but now they want to make sure the lintel is strong enough to carry the load above and want calculations.

The lintel provided has a capacity of 9.84 k/Nm
Outer skin is blocks, taken an average from website are 6.8kg each, which means with arching effect I need to take into account 6 block. Each block is 215mm x 440mm, multiplied by 6 = 0.57m2 or 3.86 kg/m2 (I think)).
I understand also regarding the safety factors of the dead loads and live loads and need to multiply the result by 1.4 and 1.6 respectively.

But I don't know how to turn this into kN for the Bending Movement calculation of BM = WL2 / 8

This is a straightforward window installation, or it should be.

I need some calculations to provide the council this beam is suitable.

Can anyone help, please!!

Thank you in advance.

Alex

 

[freddiemercurystwin]

If you know the manufacturer, some will produce the calcs for you if you provide them with adequate information, or at least Catnic do.

 

[oldbutnotdead]

As above, if you use a fabricated lintel most BCOs will be happy with the supplier documentation. Fun starts if you just want to use an RSJ of some sort, calcs nearly always required for them.

 

[^woody^]

You would use a standard timber frame tray lintel for the external wall fitted in accordance with the manufacturer's guide, and it would be approved.

The issue would be the internal support and how you are going to alter the frame, fit the timber beam, and refit the sheaving to the new beam.

 

[alexanderbourke@hotm]

If you know the manufacturer, some will produce the calcs for you if you provide them with adequate information, or at least Catnic do.

Thank you, I might have to do that.

As above, if you use a fabricated lintel most BCOs will be happy with the supplier documentation. Fun starts if you just want to use an RSJ of some sort, calcs nearly always required for them.

I've provided the Council with Declaration of Performance sheet, but still are not happy to provide the warrant.

You would use a standard timber frame tray lintel for the external wall fitted in accordance with the manufacturer's guide, and it would be approved.

The issue would be the internal support and how you are going to alter the frame, fit the timber beam, and refit the sheaving to the new beam.

I've provided all the drawing for the installation and they are happy with them, but now asking for the calculations. It's just one hurdle after another!!

 

[^woody^]

What has been approved?

If you are using off the shelf lintels in a standard situation then you don't need calculations, as they have already been published by the manufacturer.

If you plan to use a standard lintel in a non standard way, such as the internal support of a timber frame, then the inspector may well want you to justify it.

 

[alexanderbourke@hotm]

What has been approved?

If you are using off the shelf lintels in a standard situation then you don't need calculations, as they have already been published by the manufacturer.

If you plan to use a standard lintel in a non standard way, such as the internal support of a timber frame, then the inspector may well want you to justify it.

Hi Woody,

I believe I am using the lintel in a very straight forward way. It's a timber frames domestic building, a hole needs to be cut for the window and the lintel placed above. Above that room (the kitchen) is 1 other floor (bedroom / bathroom) and then a roof. I'm not sure ow straightforward it can be. I have given the information for a Supreme lintel 65h x 100w x 1500l with a load capacity of 9.84 kN/m. My builder is baffled to why they want the calculations.

 

[^woody^]

It is straightforward, but you have to be clear what you are doing.

A timber frame has a steel lintel to the outer bricks and timber beams to the inner frame. Like this

If you are intending to fit a steel lintel to the internal frame, then the inspector may be asking you to justify it, as it's non-standard.

If you are just fitting an external lintel, then just give them the manufacturers details.

 

[alexanderbourke@hotm]

Thanks Woody my builder is using a concrete lintel BTW, to be fair I'm not sure why. Maybe cost.

 

[^woody^]

Strange choice

 

[noseall]

Thanks Woody my builder is using a concrete lintel

 

[alexanderbourke@hotm]

I've provided the calculations for the lintel but now they are saying it is out with their scope of practice to verify these and I have to get a qualified professional to check over the calculations.

Maybe the window installation was not meant to be.

 

[jeds]

Concrete lintels come with a safe working load. You said 9.84k/Nm - but you meant kN/m - which is 9.84 kilonewtons per metre. For a standard concrete lintel you don't need to worry about safety factors. The lintel manufacturer has already allowed for all of that. All you need to do is add up all the load on top of the lintel (dead and live) and if it is less than 9.84kN/m it's a good un.

Easiest way to do this is find the load per m² for the materials and then work out the area? e.g. medium density blocks + render is, say, 2.25kN/m². The load area above a 1200 lintel is 0/36m² assuming a 45° load triangle. So, total load (for blocks + render) is 0.36x2.25 = 0.81kN - and that's on the total lintel. You could work out the load per m but it ain't worth it - by inspection you are massively inside. Now just work out the rest of the loads. If it gets tight - go back to the load per metre?

PS. a 45° load triangle is appropriate where the panel above the lintel is continuous with no interruptions, such as windows. In that case BS requires you to use a 60° triangle.

 

[alexanderbourke@hotm]

Thanks Jed.

I provided the calculations (I was a building student, I was a bit rusty but got there) and then they emailed this reply...

"The calculations you have provided are out width the scope of what can be assessed by building standards, however if you are able to have your calculations checked by a suitably qualified person we would find that acceptable on this occasion due to the small scale of the works."

My builder is completely baffled. He said I would have to contact a structural engineer to give the same calculations and it's just a box ticking exercise, but it would cost about £500.

It just gets you down for such a simply job.

 

[freddiemercurystwin]

Is this timber frame inner skin and brick outer, as woodys example above? Or something different?