Stick Build advice.

[saveasteading]

About to order the timber for the stick build section of new build (replacing demolished section.)

 

1. I am trying obviously to get the most efficient design to save timber and labour.

 

I can see that a kit build company brings in whole wall panels, places them on a sole plate, then straps a top wall plate on to hold it together.

 

But with stick built, can we not build the studs straight onto the sole plate, and then a single top timber (except where doubled/trebled as lintels etc)?

Saves wood, saves labour, reduces cold bridge, increases insulation area. 

I think this may just be a standard detail that is not questioned.

 

2. Any idea why there should be a dpc under the sole plate of Internal Walls? Architect and Engineer dont have it but a potential joiner's QS has included it. The wall will be on a concrete slab with dpm below it.......just checking I am not missing something.

 

3. Simpson rafter hangers with adjustable sloping foot.....cost about £18 each.   !!. x 50.  I cant see any competition to this supplier.  Know any alternative or something cheaper.

 

4, Inverness area only....where is the best timber price at the moment? The prices seem to have eased, and are about £550/m3 for big timbers. That is list price and should come way down for a big order. Do John James sell direct?  Loads of mills doing C16, but is it treated? One local mill said they can't beat the merchants and only do special commissions.

[JohnMo]

Not sure if MKM are in Inverness, but when I priced lots of timber up (Elgin) they were the best price I found.

 

I didn't include a DPC under internal walls, didn't see see any need as you also reasoned.

[MikeSharp01]

1 hour ago, saveasteading said:

But with stick built, can we not build the studs straight onto the sole plate, and then a single top timber (except where doubled/trebled as lintels etc)?

Saves wood, saves labour, reduces cold bridge, increases insulation area. 

I think this may just be a standard detail that is not questioned.

When putting up stick built you need something to keep the walls upright while you build. We used the scaffolding to do that with some internal bracing. I made some adjustable clamps so I could get it dead right by strapping the digital level to the stud and then listening for the upright tone while adjusting my little clamps. 

[nod]

It’s good practice to put dpc under gf studs 

Some companies even request dpc under metal studs 

[Thorfun]

Dpc is cheap. Why would you not just add it under internal walls? Our internal walls have a DPC and they’re above a basement! TF erectors just said they install the DPC as a matter of course. 

[JOE187]

+ ! for dpc under all plates.

Simpson rafter hangers with adjustable sloping foot.  Try metro fixings ltd.

[saveasteading]

14 hours ago, Thorfun said:

erectors just said they install the DPC as a matter of course. 

Saves thinking and they don't know the foundation design, so sensible. But we must always question overdesign, and always ask 'why', whether to save £1 or £100,000....or to invest extra for a benefit.

[Thorfun]

1 hour ago, saveasteading said:

Saves thinking and they don't know the foundation design, so sensible. But we must always question overdesign, and always ask 'why', whether to save £1 or £100,000....or to invest extra for a benefit.

yep. fair point.

[saveasteading]

6 hours ago, JOE187 said:

Simpson rafter hangers with adjustable sloping foot.  Try metro fixings ltd

A good reference thanks. Heavy straps are good value. But the rafter hangers are £19 each!  Maybe big discounts for quantity (50) and for asking?

[saveasteading]

20 hours ago, JohnMo said:

Not sure if MKM are in Inverness

Yes Inverness and Elgin. I always found them  to be fair so may send enquiry to them.

But general merchants are usually very much more expensive than specialist timber merchants from where they obtain it themselves. The timber merchant at the dockside or in the forest  should be the one. 

If ProDave is listening in,   Fettes looks a good price, considering that is price each. £420/m3 treated.

[SteamyTea]

1 minute ago, saveasteading said:

Fettes looks a good price, considering that is price each. £420/m3 treated.

So money does grow on trees.

[saveasteading]

I did some mill buildings for a Finnish timber company, owned by the foresters.  They explianed that when prices drop they let the trees grow, then when they rise they harvest. While keeping the business running of course.

[saveasteading]

The prices really have fallen. Not great, but not as bad as it was looking for a while. OSB about 40% off list. Timber ditto from a BM. That is still more than the ex-mill price quoted above but getting closer.

 

Next question.

These sloping bottomed rafter hangers.... (£17 each probably)

Any reason we can't use normal joist hangers with horizontal bottoms (£4), and notch the rafter into it?

I am assuming that rafters into glulam ridges are treated as pinned joints, and so this would be a tidy and economical solution.

(The Engineer doesn't issue any calculations without a lot more payment so there is no proof. By inspection 225 x 45 over 2.5m horizontally looks plenty for simply supported).

 

Also, as the rafters become shorter in the triangles of the valleys and hips, is there a stage at which we just bang in 4 nails?

[Gus Potter]

@saveasteading

 

Hiya.

 

My thoughts in line with your text and in green colour to give it a go.

 

About to order the timber for the stick build section of new build (replacing demolished section.)

 

1. I am trying obviously to get the most efficient design to save timber and labour.

 

Gus - Good effort

 

I can see that a kit build company brings in whole wall panels, places them on a sole plate, then straps a top wall plate on to hold it together.

 

Gus - Yes normal practice, but lurking below the surface there is a contractual reason for doing this. The TF company base their quotes and design on the assumption that dimensionally and level wise they can erect the panels on a controlled interface.. the sole plate. If the TF company are erecting they will  send their surveyor out to check the dimensions and levels.

 

But with stick built, can we not build the studs straight onto the sole plate, and then a single top timber (except where doubled/trebled as lintels etc)?

 

Gus- technically in terms of the sole plate if you look at one panel alone.. yes if what you have below the sole plate has a higher compressive strength perpendicular to the grain than the sole plate timber once you have taken into account the load spread down through the depth of the sole plate. But in practice you will often find it very difficult to comply with the level tolerance and dimensional tolerances that the TF panels require. That is one, probably the main function of the sole plate.

 

Call the top timber of the panel the top rail. Above that is another timber.. the head binder that connects the panels together. But.. the head binder serves a number of purposes. For example it adds a bit of stiffness to the head of the wall for. If one rafter is moving more than others it helps shed and share the load out. Also, the panels often work to resist sideways (horizontal) wind loads and the head binder is required to make the individual panels work as a whole rather than individually. This makes the whole system more efficient. Head binders can be long so less chance of say a truss clip falling next to a heavily nailed joint. Remember that a timber can only take so many nails before it splits.

 

Saves wood, saves labour, reduces cold bridge, increases insulation area. 

I think this may just be a standard detail that is not questioned.

 

Gus - always good to question and share knowledge. This is the only way we learn to build better, safely protect the environment. Now with modern cheep laser levels your local builder can achieve much better control over the tolerances. But!  not all builders can do this. Yes it is a standard detail but if you can design for a higher standard of workmanship then @saveasteadingmake sense. If you could remove the sole plate and replace with insulation then there is an obvious advantage. One less joint. more air tight, more insulation and less shirinkage over the panel height.

 

Oh.. timber frames shrink, the outer leaf of masonry less so. Timber shrinks much more perpendicular to the grain (the sole plate, bottom top rails and head binders) than along its length. Thus when we design TF's of two or more storeys we need to look at how we orientate the timber in the wall panels and within the floor zone (the rim beam for example) to minimise shrinkage and differential movement that jambs doors/ windows and causes other "horrible" things to happen.

 

 

2. Any idea why there should be a dpc under the sole plate of Internal Walls? Architect and Engineer dont have it but a potential joiner's QS has included it. The wall will be on a concrete slab with dpm below it.......just checking I am not missing something.

 

Gus - Good practice. If your timber is sitting on an internal concrete slab well protected with a dpm and no condensation risk then all boxes seem ticked. But if you have a burst pipe the slab could be soaked for months before it dries. Best to isolate the timber from a slab that could suffer from a plumbing problem that could compromise a major load bearing wall. The houses we are designing should last well beyond our lifetime. at some point someone will get a water leak.

 

3. Simpson rafter hangers with adjustable sloping foot.....cost about £18 each.   !!. x 50.  I cant see any competition to this supplier.  Know any alternative or something cheaper.

Ah.. generally longish rafters, can take about a 25% notch depth before shear at the ends becomes a potential issue. You could use a standard Simpson JHA hanger.. PROVIDED they are not intended to also act as ties. In the round if it is up at say ridge level you can sometimes use a cheep standard hanger and cheep steel strap to provide the tying required. You can even use a timber up at the ridge as a tie if Architecturally acceptable, you fix plaster board to same timber.. free lunch!

 

4, Inverness area only....where is the best timber price at the moment? The prices seem to have eased, and are about £550/m3 for big timbers. That is list price and should come way down for a big order. Do John James sell direct?  Loads of mills doing C16, but is it treated? One local mill said they can't beat the merchants and only do special commissions.

 

Good news on prices calming down.

 

Also, as the rafters become shorter in the triangles of the valleys and hips, is there a stage at which we just bang in 4 nails?

 

Yes it's often called loose infill, less than 1.0m length and uniformly loaded  it's pretty much infill.

[saveasteading]

All great info.   

By the time we add second and third timbers at openings the head is going to be doubled nearly all the way anyway. The proposed joiner is reworking his price after we pointed out the QS errors (better say approximations) and I expect he will do 'his way'  only.

 

Re sole plates, I have previously done 2 very large TF buildings over 4 storeys. The first TF contractor asked for a concrete kerb. We gave him a kerb of pc lintels, which quartered our cost, and they said was great but had never seen before.

The second one required a timber plate. 

 

We had lifts in these buildings and had to leave the building to settle for months otherwise the doors open at the wrong levels. So shrinkage and consolidation (gravity) action downwards was about 100mm.

 

Back to now.

Shock horror....the SE has changed the rafters to 400cc by changing a note on the drawing and not telling us. (wall studs remain 600). When asked they replied that deflection 'may be a bit too much aesthetically'.....Seems unlikely to me as 1. the design programme will spit out approved sections for strength and deflection. 2. the next section deeper will add 10% to the material and nil to labour, whereas changing the cc adds 50% to both.

3. the original roof was slate, but we are using metal.  Lighter by a distance and snow will not stick at 45deg. 4. we are adding ceiling struts/joists.

We are not entitled to calculations so have no check. however they have not referred to the Architect's design much anywhere, so likely they have allowed slates.

We are asking if 600cc is ok if we accept that there might be a droop. Such get-outs seems to be what they need

 

The hangers were the one thing under-priced so this solution brings it correct....perhaps the QS knows.

 

Loose infill is my new favourite term as it saves 24 hangers.

 

 

 

 

[Gus Potter]

I'll leave commenting on the change in rafter centres etc for another time.

 

Was on site last week and saw a lovely pile of 25 lengths or so of C24 timber 145 x 45. Builder says.. that was cheeper than C16!

 

Story goes. Everyone specs C16 the lower grade so that grade is much in demand.. merchants put the price up and don't happen to mention that the higher grade is cheeper.

 

No friends in the desert eh!

 

 

[saveasteading]

SE has agreed that 600cc is ok.

How so, only when we point this out?.  I guess on most jobs the client just pays the extra,

[MikeSharp01]

On 24/05/2022 at 18:05, saveasteading said:

Any reason we can't use normal joist hangers with horizontal bottoms (£4), and notch the rafter into it?

Yes - think about it, you are reducing the effective depth at the point where you want the max strength. You might discuss using a deeper flat hanger and putting a sloping wooden insert in the bottom to rest the rafter on with your SE.

[saveasteading]

5 hours ago, MikeSharp01 said:

at the point where you want the max strength.

Is it though? If the rafter is designed as simply supported then bending is nil here., and we are looking at shear and uplift.

As the rafter is 225 x 47 there is a lot of shear resistance, and the rafter has been chosen with limiting deflection, before structural failure is involved.

The massive glulam beam will just about hold it all down without the rest of the structure. 

These are hunches though as we have no numbers.

 

Yes we may have to ask the SE but the answers here provide us with more context from people who have done this before.

It would be nice to present a solution and make it easy for them.

As you may have read, we have already suggested several improvements to their design, and I wonder if at some stage they get the huff and say no.

I am probably being unfair saying that, and they will take it on its merits.

 

Gus thinks a notch will be ok.

I have sketched it and , because the rafter is so deep, 25% notch out should be feasible.

 

I was rather hoping that someone who has done a stick build or bought a kit with a ridge beam will know how their ridge was built.

 

 

 

[Russell griffiths]

No hangers needed for uplift or downward movement IMHO 

fit a 25x 50 batten  the full length of your ridge, 

do a plumb cut on the rafter end including a notch for the batten. 

Fit rafter and secure with a  125-150x8 timber fixing. 

 

All you need then is restraint straps, these will go over the top of the ridge and fit to the top or side of the opposite rafter. 

[saveasteading]

So Russell, is this second sketch  in line with your suggestion?

It is certainly very neat with the tiny cut-out. Joiner friendly, and avoids the expensive Simpson brackets.

I wonder if 25mm as a ledge is secure enough during construction. so perhaps a 2 x 1?

Also I guessed where the screw that holds it in place goes. with a wider batten it could go up from the bottom.

And cold feet: I have also added an angle bracket...perhaps unnecessarily.

 

The first sketch is my original idea of using a standard joist bracket, with a notch which is less than 1/4 as instructed by Gus.

Sorry about the hybrid 3d, the sloping rafter makes it tricky.

 

 

[Russell griffiths]

Many ways to skin this cat. 

If going with a hanger, no notch needed, just a saw cut for hanger to slot into. 

If going with a batten I would add a 150-175?? Construction screw through each rafter into the ridge. 

 

Restraint strap does not need to be thick. The thinner the better as it can play havoc with your roof tiling. 

Its in tension so doesn’t need to be thick, I think mine are only 1.5 —2mm. 

[saveasteading]

38 minutes ago, Russell griffiths said:

Many ways to skin this cat. 

Thanks. You think the angle plate is unnecessary then?

 

39 minutes ago, Russell griffiths said:

150-175?? Construction screw

Angled through the side of the rafter and into the ridge?

I was thinking of that as a temporary fixing, not the finished article. 

 

So downwards load is onto the batten, upwards load resistance is only  rafter weight plus from the screws....doesn't seem enough, but 8mmand a screw each side, yes that is a lot of shear.. and the timber at the screws is the likeliest failure point., so position half way or above.

Held tight against splaying by the band and the screws.

 

40 minutes ago, Russell griffiths said:

If going with a hanger, no notch needed, just a saw cut for hanger to slot into. 

How clever. Won't help the strength  but is a cut less. I will change the sketch to notch to sit in the hanger or cut to slide onto hanger base..

57 minutes ago, Russell griffiths said:

Restraint strap does not need to be thick

So use a roll of banding?   20 gauge (= 0.91mm). and lots of nails.

 

Costs will be similar for either method I think, around £4 per rafter for materials as opposed to the sloping strongtie at £17. 

Labour very slightly more?

 

We will have to put this past the SE who did the warrant, so will ask the joiner if he has thoughts then plump for one. Assuming the SE isn't familiar with traditional construction, the joist hanger is prob easier to 'sell'. But then again...local joiner says this is how to do it.....and a bloke I don't know off the internet.

[Gus Potter]

What about this? Have attached a very rough sketch.

 

Notch bottom of rafter< 25% Use JHA Simpson hangers wrapped over as you have shown. These take the shear loads.

 

Buy some flat galvanised restaint straps 2.5mm thick or round about. Get a vice and a spanner and gently put the 90 deg twist at each end where you need them to be or if you want the full bunnah get Simpson to make them for you. Try if you can to get at least 6 no square twist 30 x 3.75mm into the rafters maintaining a 20mm edge distance to the timber. Much will depend on the rafter angle, the shallower the more meat of timber you have to play with.

 

The twist strap will sit flush with the bottom of the Glulam and tie them together at this level. Get 3 - 4 sq twist nails nails up through the strap into the underside of the Glulam.

 

If you put the strap over the top of the timber you'll need to scab extra timber to the side to fix the sarking as the strap will foul the sarking nails.

 

Food for thought?

 

 

 

 

 

 

 

Edited May 30, 2022 by Gus Potter
Typo - a left handed one

[markocosic]

I typed something long. 

 

 

Short version is I like the "Gus strap" idea for spread.

 

You might want truss hangars rather than joist hangars though; or you might want the joist hangars upside down if the uplift loads are higher than the down loads.

 

 

 

Glulam is 140 mm wide and 405 mm high

 

Rafters are 47 mm wide and 240 mm high (more than 240 mm because angles)

 

 

 

Compression stops them spreading into the glulam "horizontally"

 

- cut nicely and you're done

 

 

What stops them spreading away from the glulam "horizontally"

 

- (more traditional?) roof tie between the rafters just under the ridge beam

 

or

 

- Gus strap; which is the metal equivalent of the above

 

or

 

-  nail a thin strap across the top

 

 

What carries vertical loads?

 

- (more traditional?) sit the rafters on top of the ridge beam and carry down loads in compression / use a ruddy heavy roof covering for uplift (this is not the case with a metal roof!!!)

 

or

 

- (more traditional?) sit the rafters on top of the ridge beam and carry down loads in compression / use a roof tie jammed up hard against the bottom of the ridge beam to for uplift

 

or

 

- truss hangars are in 47x97 and carry 5-6 kN each in the "wrong" direction (uplift) which ought to be plenty; all they can't do is carry the "spreading" load but you have the strap for that

 

https://www.bpcfixings.com/downloads/datasheets-new/BPC Data Sheet - MTH-240.pdf

~£1.50 ea in volume

https://www.leofixings.com/product-p/lfprodpar00140.htm

vs ~£0.50 for joist hangars?

https://www.leofixings.com/product-p/lfprodpar00211.htm

 

The truss hangars are stronger than joist hangars in the uplift. The ledger is fine for initial assembly and fine for tile load / snow load but it don't do anything useful for you in wind load. I think that the latter will be what keeps the SE up at night I imagine. He / she might even want the joist hangars to be upside down if they were used! Notching the tops of the rafters flat...

 

 

2.5 metre span though? Can't be much uplift on that!