Greetings from a practical f-wit

[Hill Runner]

Hi All

 

Have a small cottage (at about 1400 feet above sea level in Scotland) and in process of insulating underfloors and internals walls.

 

So much prevarication, so much faffing, so much finding reasons to go out running/cycling/swimming instead of getting my 5h1t together.

 

Have been speaking with a retrofit expert who quite rightly suggested I go on this forum for collective replies rather than relying on his charity!

 

So there may be questions coming up very soon, and thanks in advance for your help and acceptance.

 

Hill Runner

[saveasteading]

Welcome. There are lots of us with interest and/or knowledge in this subject. Ask away.

 

1400 ft altitude is a very long way up. So you are -3C compared to sea level  simply through altitude.

 

You don't need to tell where you are ( and perhaps best not to) , but an overview will be good with your first questions.

 

[CotswoldDoItUpper]

Welcome!

We also ripped up floors and insulated between joists etc etc. it’s fun!
Good luck!

[ProDave]

Hi and welcome.  That's high for a dwelling even in Scotland.  I can think of a few villages that high, mostly in the Cairngorms.

[Simplysimon]

welcome,

3 hours ago, ProDave said:

That's high for a dwelling even in Scotland.  I can think of a few villages that high, mostly in the Cairngorms.

don't need to go that far north, wanlockhead is above that, btw scotlands highest

[Hill Runner]

Hi All

 

Thanks for your kind words and great to hear from you all. It was -5 on Wednesday morning, felt sorry for the campers in tents at the foot of the pass! Simplysimon is spot on, Wanlockhead, Southern Uplands (also highest pub in Scotland, not as high as the wonderful Tan Hill Inn though in England).

 

Anyway I digress. Advise sought and perhaps I will post on one of the more generic forums? Is that where I should be going really? So there I was with this horrible PIR board between the joists, and after so much prevarication I'm also thinking of putting it on the interior wall that that faces outside at the front of the house. But here is the crux, I have no idea whether I can just attch it do the present plaster (looks like lath and plaster? I have a horrible feeling that you experts will tell me to get rid of the plaster and use lime somehow, but really not sure what I'm doing here. The PIR is 12cm, quite happy losing that space to make this bally house warmer. Photos with work still in progress between joists (yes, I realise now that I should have done this bit last d'oh!). Oh going to move the sockets away from that wall as well.

 

 

[Hill Runner]

Ah, just seen this on the forum:

 

 

[ToughButterCup]

6 hours ago, Hill Runner said:

...

Hill Runner

 

Welcome from another.  Well, ex - . Osteoarthritis . 68 and still a F-wit. Yer in good company Jimmie.

[jayc89]

On 29/04/2022 at 20:26, Hill Runner said:

Ah, just seen this on the forum:

 

 

I'm not convinced IWI (Internal Wall Insulation - Mod) is fully understood yet. So many differences of opinions, so many reports of people fitting IWI in ways that should cause problems, yet there's very little evidence (on the internet) of actual people having actual problems.

 

My current conclusions, which may also be entirely wrong, are;

- Moisture cannot be allowed to escape the warm rooms, through the insulation, reaching the now cold wall.

- Every effort should be made to keep the wall dry from the outside (well maintained pointing/gutters/drains, avoiding build up of external ground level etc)

- The wall needs to be able to dry if it does absorb moisture (pointed in lime, no sand/cement renders etc)

[CotswoldDoItUpper]

Nice neat job that! Enjoy the expander foam and foil tape. Tip: get the wide stuff, saves having to tape twice (both sides of the joist) and just go with one big stripe that covers the whole lot!

[Simplysimon]

1 hour ago, jayc89 said:

yet there's very little evidence (on the internet) of actual people having actual problems.

as with the first timber kits, it took quite a while to show and nowadays people are using more plastic sheeting for vcl and it doesn't show for a lot longer. i do think there will be big problems in the future with iwi and modern houses wich are 'fairly' well insulated but not well detailed

Edited April 29, 2022 by Simplysimon
missed a letter

[jayc89]

4 minutes ago, Simplysimon said:

as with the first timber kits, it took quite a while to show and nowadays people are using more plastic sheeting for vcl and it doesn't show for a lot longer. i do think there will be big problems in the future with iwi and modern houses wich are 'fairly' well insulated but not well detailed

 

How long has insulated plasterboard been around for? People have been slapping that on to solid brick walls for years now.

[Cpd]

Welcome to the forum, another ex hill runner from Argyll where I have three old stone cottages in various states of repair /  renovation,  my walls are natural sone with a rubble core. I went / am going with building timber frames on the inside, infilled with PIR and then PIR over the top of the frames and plasterboard as the final covering. Taking the detailing very seriously and aiming for very good air tightness. 

[saveasteading]

5 hours ago, Cpd said:

am going with building timber frames on the inside,

We are the same.

 

With the price of timber likely to keep rising I have an idea.....but it might be silly....so here goes.

 

Someone on the forum showed a type of timber frame, named after the inventor, made of small timbers connected by ply plates, a bit like a fabricated joist.

 

If we were to make our own, probably in a former, then we could use this for the inner liner. It would use less timber, we could buy the cheapest  £/m3 which is CLS  etc, and also break the cold bridge through the timbers themselves. Also replaces timber with more insulation in the void. 

More labour of course, so perhaps only for a diy job.

 

Also for very large quantities the price can get much better. I once bought a whole bundle of 2 x 2. (6m3). As it was straight from the docks and no handling at the depot, the price plummeted.

 

We can call it the Buildhub Stud Method.

 

Comments?

 

 

[ProDave]

I think you are looking at a Larsen Truss.  Typically two frames made of 4 by 2 joined bit strips of ply or OSB.  The main reason being to avoid cold bridging apart from the joining plates.

[saveasteading]

1 minute ago, ProDave said:

a Larsen Truss

That is the one. we have 140mm x 50 mm timber stud  in the current plan. so using 50 x 50 twice is only going to save 1/3 of the timber, now I think about it, with  a lot of work.

But CLS is lots cheaper / m3 than the bigger stuff..

Another thought...the stud assembly will be enclosed in vapour and moisture barrier, so no risk of rot or worm, and untreated timber should be ok.

[Simplysimon]

1 hour ago, saveasteading said:

That is the one. we have 140mm x 50 mm timber stud  in the current plan. so using 50 x 50 twice is only going to save 1/3 of the timber, now I think about it, with  a lot of work.

But CLS is lots cheaper / m3 than the bigger stuff..

Another thought...the stud assembly will be enclosed in vapour and moisture barrier, so no risk of rot or worm, and untreated timber should be ok.

but 50x50 is a lot cheaper than reg 145x45

[saveasteading]

3 hours ago, Simplysimon said:

50x50 is a lot cheaper than reg 145x45

I'm not so sure. the CLS and 2 x 2 used to come ready prepared from Russia so that won't be happening.

A local Highland sawmill told me they couldn't compete with these prices so they only did bigger timbers and specials.

 

From a quick look at Wickes (because the prices are  real time) I calculate that 2 x 2 is £1,400/m3 inc vat , and CLS 38 x 63 is £828/m3...a huge difference, and the CLS principle stands.

 

Another  local sawmill is quoting everything in C16 as £430 +VAT, but I suspect  the website is behind the times. That is 2 x 2 up to 8 x 2.

[SteamyTea]

@saveasteading

 

Could you make something like this.  Probably need a simple jig to hold it all in place, then glue and screw/nail.

Maybe @Gus Potter could have some input.

 

[markc]

The built up section will (assuming the glue is good) always be stronger and stiffer than one piece solid timber ‘flanges’ on a Larsen truss or I joist. Bit more fiddly to make but incredibly strong.

[MikeSharp01]

Filling in with solid insulation between Larsen Truss or I-Beams is a pain, Where we are not having blown in cellulose I made EPS 100 infills which effectively made our I-Beams flush than I could push in the 0.032 insulation batts without the folds around the step and any gaps. 

 

 

 

[saveasteading]

18 hours ago, SteamyTea said:

Could you make something like this

I was thinking of something more primitive but easier to build. Timber as the the 2 flanges, then rectangles of plywood on the sides , both sides but poss staggered.

As it doesn't have to be terribly strong, it doesn't need to be I form. 

If I could do a drawing as well as SteamyTea then I would.

[Gus Potter]

On 29/04/2022 at 19:50, Hill Runner said:

Simplysimon is spot on, Wanlockhead

Hello Hill Runner.

 

Great place, high up so next stop is the moon. I'm down the road/ hill from you but have you bought a gold pan yet?

 

If you have attended to all the gutters, down pipes etc and checked the ground levels are not bridging the DPC what about strapping the walls with 50 x 25 treated timber. Fix a bottom and top rail and verticals at 400 centres. Pack the straps off the wall say 5.0mm with a small cutting of DPC behind. How old is the house, does it have a bitumen DPC.. what is the construction of the external walls?

 

On 30/04/2022 at 15:18, saveasteading said:

That is the one. we have 140mm x 50 mm timber stud  in the current plan. so using 50 x 50 twice is only going to save 1/3 of the timber

Ah saveasteading, good point, made me think. To saw an 8 x 2 structural timber out of a 16 inch log after cleaning & stripping say requires four saw passes. But to plain saw a 2 x 2 requires another 3 passes of the saw? So more sawing to produce smaller timber out of the same size of log. But in real life the smaller logs are used for the smaller sizes. hey ho. The point is that you need more sawing? Also the surface area is greater relative to the cross section area of the smaller timber so you may need more preservative and a bit more handling? Maybe this goes some way to explaining why smallar timbers cost more than standard large ones per volume of timber?

 

On 01/05/2022 at 07:06, SteamyTea said:

Could you make something like this. 

 

On 30/04/2022 at 15:13, ProDave said:

I think you are looking at a Larsen Truss.  Typically two frames made of 4 by 2 joined bit strips of ply or OSB.  The main reason being to avoid cold bridging apart from the joining plates.

Thanks Dave for the Larsen truss, great spot and Steamy too and everyone else.

 

On 01/05/2022 at 07:53, MikeSharp01 said:

Filling in with solid insulation between Larsen Truss or I-Beams is a pain

Lastly to Mike, but setting aside a real good practical point from Mike and for a bit of fun I have had a look at the Larsen truss, how it works to some extent in terms of creating a twin wall so you can create depth for insulation. I've tried to capture some of the main points but..!

 

On 01/05/2022 at 07:17, markc said:

The built up section will (assuming the glue is good) always be stronger and stiffer than one piece solid timber ‘flanges’ on a Larsen truss or I joist. Bit more fiddly to make but incredibly strong.

Mark et al please chip in if you think I have missed something or made an error as no point in posting incorrect stuff.

 

Here goes.

 

I'll put some qualatative numbers to this. Work out the weight of the cladding, say another layer of OSB, battens and some timber shiplap.

 

Shiplap thickness 14 mm. Timber density = 420 kg/m cube 0.014 *420 = 5.9 kg/ m sq

Vertical 50 x 25 battens to create gap between board and OSB @ 400 centres. 0.05 * 0.025 * 420 / 0.4 = 1.3 kg / m sq

OSB 9.0mm thick 5.5 kg / m sq.

 

Sum of above = 5.9 + 1.3 + 5.5 = 12.7 kg per sq metre.

 

Convert kg to kilo Newtons 12.7 * 9.81 * 0.001 = 0.12 kN add say 25% for "other stuff" like insulation and self weight give 0.15 kN per sq m.. not a lot as 0.15 kN is about 15 kg per sq metre.

 

Over a 2.4m height this gives a load per metre run of wall of 0.15 * 2.4 = 0.36 kN ~  37 kg. Now because the cladding is off centre from the point of support it causes a bending effect in the vertical section. The bending effect (the bending moment will be ~0.15 * 0.4(lever arm) = 0.06 kNm this is very small. For example if this was a domestic floor engineered I joist we design for the dead loads (self weight, flooring plaster board etc) and live loads, you and others. The live load is 1.5 kN/m^2 (~150kg) for a domestic floor so the bending moment is calculated for the uniformly loaded floor joist under live load space at 400mm centres as follows. Spacing * Load * length squared /8 =0.4 * 1.5 * 2.4/ 8 = 0.432 kNm which is more than the above bending force from the cladding weight. You can see that the bending effects from the cladding weight probably don't govern the design.

 

Look now at how the cladding weight gets to the point of support. For every run metre run of wall we have about 0.36 kN..(36 kg) of cladding etc not a lot. There are battens at 400mm centres so each batten has to transfer via the nails 0.36 kN *0.4 = 0.14 kN over it's height. A very small amount. Now a 2.7mm diameter nail from 9.0mm OSB into a C16 grade timber has a shear capacity of some 0.05 to .08kN capacity. So the minimum number of nails will be 0.14 / 0.05 = 3 number. Again you can see that you don't need many nails to do the job to transfer the cladding load via the battens to the 50 x 50. We can set that aside for now. If using a cement board say we may need to revisit.

 

But there is no free lunch! Firstly for it all to work the load from the cladding goes into the 50 x 50 but if you only have 3 nails up the height the 50 x 50 will bend like fury and it won't work. For it to work as a truss / I joist you are looking at nails at 100 - 150mm  centres to connect the OSB to the 50 x 50. Then you are on the ball park. You may have a wind load acting on the cladding and this has to be resisted. Wind loads could be 1.0 to 1.5 kN/ sq metre so they have a big effect, much closer to a floor joist type live loading. This could often be the governing factor in the design.

 

Lastly as @MikeSharp01 points out there are practical things that need consideration, how do you fit the insulation, what type and so on. Also, you want the 50 x 50 to be stiff, you don't want to be trying to fix cladding into a small timber that bounces all over the place. I think that although you can show that the forces can be accounted for structurally and you can "technically design" something lean you need to look at this in the round, particulary the buildability, labour cost and how easy it is to achieve a consistent quality of workmanship. I think this is the key to getting this to work.. is the practical buildability side.

 

That said it's a great concept to consider if you want to achieve low heat losses.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[MikeSharp01]

18 minutes ago, Gus Potter said:

But there is no free lunch! Firstly for it all to work the load from the cladding goes into the 50 x 50 but if you only have 3 nails up the height the 50 x 50 will bend like fury and it won't work. For it to work as a truss / I joist you are looking at nails at 100 - 150mm  centres to connect the OSB to the 50 x 50. Then you are on the ball park. You may have a wind load acting on the cladding and this has to be resisted.

Other than thinking that a properly constructed Larsen truss is practical and therefore structurally OK I cannot comment further on them. On construction - our I-Joists are glued, so the flanges are grooved and the web (9mm OSB) is glued into the groove under pressure (in the factory) so no nails. Where we do have nails (and a lot of them into the flanges) is on the sheathing on the cross walls. 3.1mm dia nails at 50mm centers everywhere for racking strength. So I guess our SE must have thought that that racking issue was the biggie.

[joe90]

As I like dealing with wood rather than concrete etc and I found @Gus Potters post above fascinating (even if I don’t understand the numbers 🤷‍♂️) however 

44 minutes ago, Gus Potter said:

Firstly for it all to work the load from the cladding goes into the 50 x 50 but if you only have 3 nails up the height the 50 x 50 will bend like fury and it won't work.

But the cladding will be pushing against the edge of the OSB due to rotational  forces and fixed to the 50 x50 so It won’t bend (well it might bend outwards if negative air pressure is great 🤔).  But realistically anyone is going to nail at 150mm centres and may even glue as well so I think the Larsen truss is a great way of building a wall that will allow a lot of insulation (maybe I might do another build 🤔) (maybe not).

 

also if the 50x50 is a bit bent (as a lot is) it can be straightened to meet the straight edge of the OSB prior to nailing.