Rafter to structural studwork connection?

[ashthekid]

Hi,

 

I have parted companies with my contractor who has left me in a bit of position to take over the project and I wanted to check with the experience of people on this forum what their thoughts were on how my timber frame is connected and if it would pass building control regulations for example.

Where the timber rafters connect to the structural load bearing stud wall, should there be any kind of metal plate connector tying them in together?

I attach a photo to show what I mean. 

Is there anything else in the photo that looks incorrect?

The plywood you see at the back is the box gutter.

 

[Marvin]

If this was my work I would be fixing metal plates on each one.

 

 

The ones I would personally use:

 

 

[Marvin]

 

 

Not impressed with all the fixings through the roofing felt either. ☹️ 

 

 

[ashthekid]

Yes don't get me started on the nails through the felt @Marvin

 

What are those brackets called in the second image of yours?

[Marvin]

  On 09/11/2021 at 18:24, ashthekid said:

Yes don't get me started on the nails through the felt @Marvin

 

What are those brackets called in the second image of yours?

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Typically: Galvanised Truss Clip 47 x 110mm toolstation, screwfix etc...  about 50p each.

 

Good luck

 

Marvin

 

[MG-Wales]

Hi, a truss clip can be used, as others suggest, just to be on the safe side but it is not strictly necessary. I'm a structural engineer and I work mainly with timber frame structures: we specify truss clips only when the wind uplift force is quite high (windy locations, shallow pitched roofs) and the dead load is low (e.g. lightweight roof covering). Otherwise rafters birdsmouthed to the top plate and fixed down with a pair of skew screws/nails would be providing an acceptable nominal connection. 

[ashthekid]

@MG-Wales As these are not birdmouthed as suggested would I still need the truss clips?

 

And does the top horizontal timber that the rafters are sat on needing to be double timber or is the single enough?

 

All I want to make sure is just that everything is safe, secure and would more than pass any building control inspection. I'd rather go over the top and feel better about it.

[Gus Potter]

  On 15/11/2021 at 20:23, MG-Wales said:

Hi, a truss clip can be used, as others suggest, just to be on the safe side but it is not strictly necessary. I'm a structural engineer and I work mainly with timber frame structures: we specify truss clips only when the wind uplift force is quite high (windy locations, shallow pitched roofs) and the dead load is low (e.g. lightweight roof covering). Otherwise rafters birdsmouthed to the top plate and fixed down with a pair of skew screws/nails would be providing an acceptable nominal connection. 

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Hello MG_Wales

 

Welcome to BH from me as a kindred spirit!

 

Gus

[saveasteading]

I am not one to add unnecessary work, but I would use these clips. You have some doubts about the build quality, so this would be  a small insurance, and you can relax on a windy day.

 

And fill the gaps in the PIR.

[MG-Wales]

  On 15/11/2021 at 21:41, ashthekid said:

@MG-Wales As these are not birdmouthed as suggested would I still need the truss clips?

 

And does the top horizontal timber that the rafters are sat on needing to be double timber or is the single enough?

 

All I want to make sure is just that everything is safe, secure and would more than pass any building control inspection. I'd rather go over the top and feel better about it.

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The truss clips of the type shown by Marvin are to restrain any uplift (wind) force whether the birdsmouth joint is to provide enough bearing for the rafter over the wall top plate under vertical downward forces. If the rafters aren't birdsmouthed you could potentially have very concentrated forces causing "crushing" on the timbers (rafters and or top plate failing in compression perpendicular to the grain). In this case I would recommend to fix a timber fillet under the rafter and making sure everything is fixed together. There are other connectors (wedge shaped) which can do both up an down forces but I can't find an example right now.

[Gus Potter]

These are worth having a look at. Also Sabre fix do a similar product and a few others.

 

Often I'll spec these on an extension where I'm using the roof to stop a long TF wall moving at the head horizontally, either outwards when you get wind suction, inwards when wind pressure and in both cases you can get quite a bit of wind uplift with a shallow pitch roof. You put one bracket each side of the rafter (still with the birds mouth to get the bearing of the timber) staggered so the nails in from each side don't clash.

 

One good thing is that these brackets have a manufacturer declared performance to resist load in three directions. For an extension the extra cost is marginal compared with the savings you can make else where from time to time.

 

I agree with MG about the skew nails but in this modern day an age your there are fewer joiners that actually know how to skew nail properly. Most just use the nail gun, the wrong nails, don't really take care to look at the grain of the timber at each junction.. they just hash on. The brackets are more idiot proof.

 

 

 

 

[MG-Wales]

  On 15/11/2021 at 21:41, ashthekid said:

@MG-Wales

And does the top horizontal timber that the rafters are sat on needing to be double timber or is the single enough?

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Sorry, I missed the second question.

 

As the rafters seem to be in line with the studs below, you wouldn't necessarily need a second horizontal timber (the so called "headbinder"). If in other locations rafters and studs are staggered, then it should be assessed: one timber rail may be enough, but two timbers are what we would usually expect.

Edited November 18, 2021 by MG-Wales
Grammar

[MG-Wales]

  On 18/11/2021 at 20:33, Gus Potter said:

These are worth having a look at. Also Sabre fix do a similar product and a few others.

 

Often I'll spec these on an extension where I'm using the roof to stop a long TF wall moving at the head horizontally, either outwards when you get wind suction, inwards when wind pressure and in both cases you can get quite a bit of wind uplift with a shallow pitch roof. You put one bracket each side of the rafter (still with the birds mouth to get the bearing of the timber) staggered so the nails in from each side don't clash.

 

One good thing is that these brackets have a manufacturer declared performance to resist load in three directions. For an extension the extra cost is marginal compared with the savings you can make else where from time to time.

 

I agree with MG about the skew nails but in this modern day an age your there are fewer joiners that actually know how to skew nail properly. Most just use the nail gun, the wrong nails, don't really take care to look at the grain of the timber at each junction.. they just hash on. The brackets are more idiot proof.

 

 

 

 

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These brackets are great (from a structural engineer point of view). I think Simpson ST makes a stainless steel version as well which is great and gets specified a lot with Oak or for external use.