3-ply timber lintels

[SillyBilly]

I am ordering materials for a self-build annexe.  The studwork is eased 47x150 which I am told is  reduced in each dimension.

I am puzzled as to what to use for the timber lintols.  I was planning to use 3-plys of the same as the studwork bearing on 1 stud for 1200mm openings, on 2 studs 1800mm, and 225mm bearing on 3-studs for an opening of 2700mm.

I have attached 2 pics showing my concern.  My Builders Merchant has standardised on eased timber which leaves a gap as in a picture taken from the construction of another house.  The alternative is to find a stockist of non-eased kiln dried lumber which would give a 3-ply lintol as in second picture.  What do  people recommend.  Is the gap allowed?

[nod]

I’d throw it at the SE

BC are sure to want a drawing 

[Russell griffiths]

As above what does it say on your bc drawings. 

I doubt very much if you can use timber over the 2700 openings, I think it will need to be steel, the deflection in timber will be huge. 

I also don’t think the 150 deep timber will be enough for any of the openings, the strength is in the depth of the timber, I would have thought 225mm would be better. 

[SillyBilly]

1 hour ago, Russell griffiths said:

I doubt very much if you can use timber over the 2700 openings, I think it will need to be steel, the deflection in timber will be huge. 

I also don’t think the 150 deep timber will be enough for any of the openings, the strength is in the depth of the timber, I would have thought 225mm would be better. 

I am studying an actual construction of 4 houses.  Pics from 2 of these show the 225mm 3-ply timber lintels over 2.7m openings

[Russell griffiths]

3 hours ago, SillyBilly said:

I am studying an actual construction of 4 houses.  Pics from 2 of these show the 225mm 3-ply timber lintels over 2.7m openings

Maybe, but that doesn’t make it right. 

Have a look at a topic on here of window heads deflecting and stopping the sliding doors working. 

Looking at those pics,there’s not a lot I like really, just stand issue poor timberframe construction. 

 

If your happy following that then then just rip a plywood packer to make up the difference. 

 

 

 

Edited June 13, 2021 by Russell griffiths

[SillyBilly]

Hi,

I take your point but both examples were on architect designed houses and had BC approval. In my case the 2.7m window will be in a single storey  lean to part of the extension so deflection isn't a concern to me. 

With my builders merchant only stocking eased regularised KD timber I need to know what to search other suppliers for.  What standard size timber headings would have been used in  the gapless case in  my first pic?

 

I have already faced inflationary rises in my project which is why I am trying to order the timber

[Nickfromwales]

Also note the additional shoulder of stacked vertical timbers taking the downward forces at the ends of the lintels . A very important detail. 3 a side in one of the pics.

If it were my house, it would be steel without hesitation. That can sit atop the same shoulder of timber uprights, so only very minimal uplift in cost, but belt and 15 braces if flying over large sliders. 

[Temp]

Timber lintels were used for hundreds of years and many modern buildings use laminated timber. They can work fine if correctly specified but thats the issue. Normally the designer would specify the make up of the lintel laminations and how they are fixed together and supported at the ends. Those details are important. 

 

47 x 150 Eased is typically 45 x 145mm. So three would be 135mm with a 10mm gap. I wouldn't think its an issue as less than 7 % gap but we are comparing varieties of apple when the designer might require bannas. Who has checked 3 x 47 x 150 is adequate? Its not good to rely on the BCO.

[Nickfromwales]

If there’s a 10mm gap, go concrete solid and fit a 10mm blade of steel plate to create a Flitch beam and put your worries to bed. You could park a car on that. 

[Gus Potter]

Hello SillyBilly.

 

Well done picking up on the arrangement and timber sizes.

 

In pic two at the top of the thread you can see there is a gap between the outer ply and the two inner ones. Now it may be that the two inner timbers are enough to carry the load and the outer one is just a "filler". But when you design timber lintels you can "enhance" the strength and stiffness in recognition that the plys are acting compositly.. together. For example in the BS code you can increase the capacity of the timbers in bending say by ~10% and the stiffness of 3 plys by ~21%. The "strength" part is to do with making sure the timber does not "break" under load".. the stiffness property (Young's modulus.. E) is to do with how much the timber will bend. Members posted a while ago about this and deflections over the heads of bifolds / sliding doors a while ago in the thread " Issues with sliding doors" Some of that post be be of use to you.

 

Link here

 

 

The key here is to recognise that to get an extra bang for your buck the lintels need to be fixed together (no gaps) say with 4.5 x 100mm galvanised nails top middle and bottom at 300mm horizontal centres. If you are using say a C16 / 24 timber grade then the overall thickness will be ~ 135mm and as Russell says you can use a timber ripping on the inside to make the wall flush on the inside for the plasterboard. This is common practice.

 

If your flat roof joists don't span onto the timber lintels then 3 ply 225 x 45 timbers effectively spanning say 2.8m ( 2.7 + 1/2 rest) supporting say typically a 1.0m wide strip of flat roof (only) has a good chance of working with an over all deflection of some 6mm. Some of that will take place under the self weight of the roof before you fit the doors, the rest due to roof access loadings, snow and a bit of creep in the timber.

 

 

 

 

 

 

 

 

Edited June 14, 2021 by Gus Potter

[scottishjohn]

maybe a help -maybe not 

we had a problem in a building where we needed to fit an RSJ  due to someone cutting the roof trusses and removing an internal supporting  wall

-but the weight and where it needed to go --as in it had to be hand balled in to a roof space  and then moved to support the roof  was too much 

 answer our builder came up with -which is still in place 40 years later was a plywood box beam - he remembered from his uni days when doing structural calculations 

half the weight of an RSJ + could take same load

this plywood box beam was from memory about 15ft long

basically 1/2" proper plywood ---four sides with zig zag internal top  to bottom  also made from the same plywood 

all glued and screwed together

 

Edited June 14, 2021 by scottishjohn

[SillyBilly]

Hello Gus

Thanks for your helpful comments and the sliding window link which I couldn't find.

I dont want  to use steel.

I have investigated further and it would seem that BM have for many years all standardised on eased regularised timber which caused my concern.  Only Houghton Timber say they have sawn but not eased timber which I may use.  I guess the installer of the one I pictured had found such a supplier.  The other one didn't bother but I wanted no gaps in the lintels hence  my original post

If I find Houghton Timber dont have any non-eased locally I will use C24 timber with a ply filler. I have increased the heights of the header lintels where 150 to 175mm.

[SillyBilly]

For Hougton read Howarth!

[SillyBilly]

Turns out Howarth-Timber don’t have any sawn non-eased timber so it will have to be a ply infill.

 

Quoting Craig
The key here is to recognise that to get an extra bang for your buck the lintels need to be fixed together (no gaps) say with 4.5 x 100mm galvanised nails top middle and bottom at 300mm horizontal centres. If you are using say a C16 / 24 timber grade then the overall thickness will be ~ 135mm and as Russell says you can use a timber ripping on the inside to make the wall flush on the inside for the plasterboard. This is common practice.
If your flat roof joists don't span onto the timber lintels then 3 ply 225 x 45 timbers effectively spanning say 2.8m ( 2.7 + 1/2 rest) supporting say typically a 1.0m wide strip of flat roof (only) has a good chance of working with an over all deflection of some 6mm. Some of that will take place under the self weight of the roof before you fit the doors, the rest due to roof access loadings, snow and a bit of creep in the timber.

 

My extension is to have a timber single storey section in which there will be a 3-panel 2.7m sliding (not bifold) door in a 5.3m timber wall.  The roof loading will be modest as there will be a 30deg warm roof with edpm not tiled top.  Some of the rafters at 600mm centres will bear on the lintel.

Can you hazard a figure for the deflection if I glue and screw the 3 plys?

 

 

[Russell griffiths]

When I had my sliding door measurements taken the surveyor would only take a measurement allowing a 30mm clearance at the top, even with all my moaning he insisted that they would not supply a door unless this clearance was adhered to. 

I would suggest you allow  a 20mm gap over the doors, this should not have any timber packers in it. 

[Nickfromwales]

2 hours ago, SillyBilly said:

Can you hazard a figure for the deflection if I glue and screw the 3 plys?

Nobody can “hazard a guess” at that ! It’ll need full SE input via calcs and those produced in a recognised format for conveyance to your BCO.

You can get general advice here, not a replacement of your SE   

@Gus Potter makes a great point about the 3 timbers needing to be as one. You can then centralise the trio and make up the same deficit in ply each side.

@SillyBilly to quote another members post just click on their text and highlight it. You’ll then see a white box with quote in it, click on that and it will open that in the editor.  

Also to ‘mention’ another member just type the @ symbol and start typing their user name. A drop down list will appear, and simply select from that. ?

[SillyBilly]

Using Quote gives me the whole of a post not the bit I want.  I couldn''t find a way to delete the link!

[Nickfromwales]

1 hour ago, SillyBilly said:

Using Quote gives me the whole of a post not the bit I want.  I couldn''t find a way to delete the link!

Don’t press the quote button   

Instead, just click on and select the required text snippet from a members post. When you finish selecting you’ll see a small quote box  appear, click that and the text will jump to your editor box ?.You can do that a number of times in the same reply so quoting multiple members ‘snippets’ in one post. 
 

Edited June 15, 2021 by Nickfromwales

[TonyT]

Instead of nails can you use serrated washers and flat washers with bolts?

[Nickfromwales]

14 hours ago, TonyT said:

Instead of nails can you use serrated washers and flat washers with bolts?

I prefer resin glued and construction screws just short of the width of 2 timbers / layers. Fix 2 together, flying and clamping and working from one end to the other so you can manipulate the timbers with additional clamps as you work along the length, then add the 3rd timber repeating the same method. The construction screws allow the timbers to be pulled together incredibly tightly, thus ejecting the excess of the resin glue, plus, combined with the info below, you should be able to marry the timbers to pull each other back to a straight pair, if so necessary. 
Examine the timbers for the ‘cup’ lengthways and sidewards and laminate them strategically to get the best overall uniformity. The lengthways cup should be strictly observed in any installation / scenario with the natural ‘deflection’ ( cup ) sent upwards so the cup naturally straightens out upon own weight and subsequent bearing of loads from above post installation. 

[SillyBilly]

Thanks.  I was going to use PVA woodglue - is that resin based?   Do you have a link to 'construction screws' ?

[scottishjohn]

2 hours ago, SillyBilly said:

Thanks.  I was going to use PVA woodglue - is that resin based?   Do you have a link to 'construction screws' ?

nope -not a resin glue 

[SillyBilly]

I had looked at Evo-Stik Exterior Resin W Wood which is a one-part resin glue but the datasheet says Modified polyvinyl acetate emulsion (pvac).  Someone like to recommend one? Should it be a two-part one?

Cascamite?

Edited June 16, 2021 by SillyBilly

[Nickfromwales]

Plenty good enough 

[SillyBilly]

On 16/06/2021 at 09:24, Nickfromwales said:

I prefer resin glued and construction screws just short of the width of 2 timbers / layers.

Is this what you mean by construction screws?