K78

Portal Frame House

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I have seen a few threads on here regarding converting existing portal frames into houses. But none on building with a new one like the barnhaus concept. 

 

Would it be a issue getting a house like this to meet building regulations?

 

It looks like a huge saving in foundation cost. 

 

A steel portal frame would cost less than my quotes for feature trusses.

 

https://nacsba.org.uk/wp-content/uploads/2013/10/images_shoestring_18_shoestring13_ed-green.pdf

14043AFC-1EDD-4A81-9357-5956C9EE29D3.png

540B5C7C-7D1E-4179-AFAA-2C88165E6D73.png

55AFEBFB-CF96-497F-822A-C9970D970690.png

Edited by K78

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This is the sort of design we are planning to use. I cannot see an issue with building regs as this is how many new offices are built.

 

What were the concerns you had about the regs?

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We are building with a new hot-rolled steel frame like this, though technically it is as a part of a 'conversion'. Frame supplier is one that usually builds barns and sheds.

 

AFAIK there is no inherant building regs issue with a hot rolled steel frame and loads of buildings of all kinds are made this way, though it will need all steel protected from fire e.g. by being enclosed or intumesent painted.

 

The Barnhaus is an interesting concept to provoke discussion, and I think in general these kinds of building methods should be more widely considered for residential, however I'm skeptical about the barnhaus pricing and some of the details. I'm not clear whether the specific design has been ok'd from a structural, insulation, or longevity perspective. The steels are whopping thermal bridges which might lead to condensation problems, and the combination of straw and steel seems dubious and a gimmick. It's unclear how they'd planned to insulate the roof. Better I would have thought to have the insulation layer on the exterior e.g. via standard insulating sandwich panels like the Kingspan KS1000RW (which we are using).

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Hi Kxi

 

I would love to see or hear more about your project. We plan on using a hot rolled portal frame with ks1000rw roof and possibly walls. May use a different profile on walls depending on planners. 
 

How do you plan on building your walls?

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@PDR

Some overall background on our project - before we had settled on a build method.

https://forum.buildhub.org.uk/topic/7201-hello-from-berkshire/

 

Steel frame with KS1000 cladding was definitely not what we started out considering, but various constraints pushed us that way and now we are committed - but nothing actually rising out of the ground as yet. We considered I think every building method known to man. To be honest at the stage you are at - I would not get wedded to a given build method. Realistically the planners only care about the outer skin rather than the internal construction.

 

The overall build method:

  • Hot rolled steel frame with a first floor of hollowcore + structural topping. 
  • Roof and first floor walls clad with KS1000RW 150mm quadcore - so the thermal and airtightness layers wrap around all the habitable parts of the building (mainly the exterior). I.e. first floor walls from outside to in: kingspan panels (150mm) - big empty space - inner plasterboard. So it is still fairly simple at least
  • Ground floor walls are non-supporting (steel frame does the support) and are block skin with timber frame inside infilled with PIR - our ground floor walls can't be kingspan panels as they have to have fire compartmentalisation against some barn areas (which likely won't apply to you)
  • First floor soffit and ground floor over slab insulated with something like Kooltherm - again - the thinnest we can manage
  • Loads of giant pad foundations set deep in the ground (we're on clay + chalk and also have to go below the existing building foundations), then a big slab over the top of that

 

Reasons why we went with steel frame + cladding:

  • Head height - planning means we couldn't go up and so we needed to save every cm we could and the KS1000 is about the thinnest super insulated roof we could get. Though we're actually now putting it on huge wooden purlins so it's not that thin... Also a mass timber frame like glulam would have meant beams that were far thicker than steel and so head height problems.
  • Concrete first floor - a large part of the ground floor is agricultural use - so could have all sorts in there. So we wanted a very solid fire seperation between ground and first floor - so concrete. Again desperate to save head height so the hollowcore is arranged set into the steel beams rather than sat on top of them in a 'slim floor' approach - they usually use this on very tall buildings to get 11 floors rather than 10. A concrete floor is most simply done with a big steel frame, though there is some interesting stuff being done with wood+concrete composite inc CLT - this was tempting but is a bit experimental.
  • Single supplier - we wanted a single suplier who could do multiple parts of the main structure because that gives a comfort factor to a first time self builder like ourselves. Steel frame + cladding is a common package. As it was we really did try engaging with suppliers of other systems - especially timber frame - but we were generally too odd a project I think and most didn't seem to want to engage
  • Cost - we're getting the frame and cladding built by a firm that makes maybe 200 giant sheds a year. In theory this should be a cheap approach and working with suppliers who work to clear and slim margins. However, some of the issues applying the method to a house mean more money needs to go on designing details and other things. We are not a simple single storey portal frame, I suspect if we were you could get it down MUCH more cheaply. Weight is also an issue - a more lightweight timber frame would probably have been cheaper groundworks. Using the KS1000 in particular has big savings for the roof - the whole roof envelope is probably less than most people would pay for just a roof covering (e.g. tiles or metal sheet) BUT this isn't perhaps a huge cost in the grand scheme of things
  • Apparant neatness & simplicity of envelope - the cladding seems an elegant and simple way of achieving everything you need in a building envelope. So simple! But, as it turns out it's simple if you want to build a giant single-storey windowless shed. Not so simple for a house...
  • Design - luckily we don't have too many 'visual' restrictions from planning and we actually like the industrial nature. I.e. the look of steel + cladding was not a barrier to us, but might be for others

I suspect had we not had some of the constraints we did, we might not have picked this method, but we might have.

 

Some problems & solutions:

  • windows and doors - putting proper windows in the KS1000 and having them thermally decoupled from the frame - complicated. Maybe it's just as complicated as in any well insulated and airtight house, but it seems no-one has done it before and everything feels like you are designing the first space shuttle. We are going to use the Kingspan DLTR 150mm 0.8U rooflights in quite a few places - you CAN flash in 'normal' rooflights, but it's hard and what we wanted (glass roof areas) was not going to be simple at all
  • thermal bridging - our very weird mixed-use shape means we have numerous giant steel beam thermal bridges through the insulation layer. This is handled with liberal use of armatherm structural thermal breaks, so it's not impossible - just a constant thing to be aware of
  • architect familiarity - Unless you get a shed builder to design it, your architect will have never worked with anything like this and there will be a lot of learning which adds cost and risk. They may just flat out refuse, not least because it reduces the flexibility they have to do architecty things. (You not be using an architect I suppose)
  • Detailling quality - in particular the flashings - these all look kind of like an industrial unit - and there's not much you can do about it. If you like that great - but you can't really change your mind later
  • Limited on what you can attach to the panels - they are thin steel sheet so attaching stuff to it is problematic. For example we want a few large awnings attached for shading, and we have to create thermally broken brackets back to the main frame, which then poke through holes cut in the kingspan panels - it's not ideal. I.e. you have less flexibility about sticking on lights and stuff. Perhaps not a big deal
  • Wall depth - the panels are nice and thin for the whole envelope - but they have got to be attached to cladding rails, then these cladding rails need to be attached to the main frame. In a warehouse generally everything is left open on the inside, but in a house you will likely want to cover this all up - so your 150mm wall which gives a 0.12U ends up being a 350mm wall anyway just it's mostly hollow. Not a huge issue, but just worth remembering that just because the panel is thin, doesn't mean your wall will be
  • Damage - the panels can get damaged by people bumping them and they are not repairable in an invisible way. I think you often see people putting brick skins in high traffic areas or on the ground floor to reduce ground level damage. As it happens we can't use them at ground floor level any due to fire compartmentalisation issues - which I suspect a normal detached house would not have an issue with
  • Resale - metal clad walls are very uncommon on houses in the UK and I suspect would impact ease of selling. I'm sure some people would think it was great, but others might not. In the US you'd probably have less of a problem. We aren't ever going to sell, so it's not a consideration. It probably depends on how much you mind about creating a building that is unusual. 
  • Baked - Browsing the forum you will also see a potential issue with decrement delay if using these kind of panels, but....we judged (but did not calculate) that issues such as good solar shading are probably more important. I guess we can report back next year whether we've been cooked or not.
  • Sound - kingspan panels provide little sound insulation - that's not an issue for us

So in short - it might be better to think of something other than KS1000 panels for the walls if you can. You will still want to have the insulation on the outside of the steel frame though (though one buildhubber - Ian built his timber frame barn conversion inside and existing steel frame). From a planning POV i don't know. I suspect a metal roof wouldn't cause much objection, but metal clad walls might raise more eyebrows - but i wouldn't want to pre-judge it as there are so many factors there.

 

Overall, I'd keep an open mind about build method at this stage. Timberframe (e.g. twin wall), CLT, and mass timber (e.g. glulam) all other interesting options to consider and you could still end up with KS1000 for the roof, or metal cladding all over if you wanted.

 

 

Edited by kxi
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I'm currently working on a conversion of a two storey barn into a house for someone - we are just about to get the building warrant approval for it (just need to show a 10,000ltrs water storage tank)

 

I'd say the main issues we've had are easy to avoid with a new build, they're more conversion specific.

 

So the biggest issue we've had is really getting an engineer to prove that the structure is suitable (we didn't have access to the original drawings or calculations from the manufacturer) but we found that the foundations weren't what they should be and the ground floor slab wasn't thick enough either.

Then the timber midfloor wasn't properly supported.

 

Putting opening rooflights in seems to be an issue, all the panel manufacturers are very resistant to that (although this place has two already installed!

 

My biggest worry is the thermal bridging over the portal itself, as we aren't using an isulated panel system, we're effectively building a new insulated inner leaf which will take the windows etc too...

 

and then we have the buildability side of how to put it all together!!

 

however, it'll all be worth it in the end, the views from the place are amazing!

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Wow @kxi thanks for the comprehensive reply. Maybe I should have said, our reason for choosing steel frame and ks1000rw is because I am a steel and cladding designer/detailer. So I have an adavantage and will do all the design work and drawings. Brother in law owns a fabrication shop and my brother in and industrial Cladder. So many advantages.

 

we are looking at making the walls narrower by fitting the cold rolled rails between the columns, then we will use a metal stud internally for the plasterboard fixing... we hope.

 

You are correct about opening roof lights. No one likes them in the industry, but you can do them and if you are doing that I have a contact who is pretty much the best of the best at fixing and sealing them, so happy to pass details if you need.

 

For your floor did you look at a metal deck with concrete as an option too? Nothing wrong with precast, I do think deck and slab is cheaper though.

 

thanks 

PDR

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On 03/07/2020 at 00:33, PDR said:

I am a steel and cladding designer/detailer

 

Ah.

I'll be asking you lot of questions then.

 

On 03/07/2020 at 00:33, PDR said:

we are looking at making the walls narrower by fitting the cold rolled rails between the columns

 

Yes, that's our plan, but it still leaves a large void (200mm ish?) between the external panels and internal board that I can't help thinking should be better used. 1,000 small cupboards perhaps. There's also the issue of dealing with flanking sound coming through the void between the rooms, so we will either try and bring the stud walls 'into' the void, or stuff it with something at the internal wall junctions. Havn't really though about that yet.

 

On 03/07/2020 at 00:33, PDR said:

For your floor did you look at a metal deck with concrete as an option too?

 

Yes, but went with precast for perhaps not good reasons. Our main aim is to reduce head height and with precast I found the 'slim floor' method to sit the precast level with the steel beams. With precast sat on the bottom flange of the beams. e.g.

 

image.png.281f79422112b679acb7e8f2a6ea2b4e.png

 

I saw this first with precast and I think the combination stuck with me. A metal deck with cellular beams version:

https://www.kloecknermetalsuk.com/westok/products/ultra-shallow-floor-beam/

 

I think I was keen on precast hollowcore because:

- I was (naively) concerned about longevity of a metal deck vs precast i.e. once the exposed metal starts to go, presumably that's it? I suspect this isn't an issue in reality. The first floor will be over an agricultural space but it's unlikely to ever be a corrosive environment like cattle, but precast felt safer. The soffit is in any case covered by 150mm of insulation and fireproofing

- It may have been we could get a slightly thinner floor with precast - don't remember

- The idea of how hollowcore works was so clever that it was seductive

- I never costed the two - had I done so things might have been different, but precast didn't seem so expensive to be a problem

 

On 03/07/2020 at 00:33, PDR said:

roof lights. No one likes them in the industry, but you can do them and if you are doing that I have a contact

 

That's very helpful thanks, though I think now we mentally switched to the KS1000 DLTR 0.8s we will probably stick with them. We only need light not ventilation. The plan wasn't for regular opening rooflights but for a 1x20m strip of glass roof set above a long corridor. The plan was to use lamilux PR60 glass roof set into the panels for this, but 

a) expensive

b) lots of teeth sucking about how to fit it. There was a solution but no-one was confident (see below)

c) big solar gain problem that can't easily be mitigated

 

image.thumb.png.6487d2cd99c466b44b502d0fa7bb5c15.png

 

 

So we're instead planning on using 6 or so KS1000 DLTR 0.8 panels. You really can't see through them, but they are much cheaper and easier to fit, and have a diffuse light without as much solar gain.

 

 

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@PDR checking notes, it looks like the SE was slightly keener on precast than metal deck for the 5m spans we needed, in terms of overall weight and and thickness required, so that probably influenced it. Metal deck needed propping for 4 weeks but that wouldn't have been an issue in our case.

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On 20/04/2019 at 17:27, K78 said:

I have seen a few threads on here regarding converting existing portal frames into houses. But none on building with a new one like the barnhaus concept. 

 

Would it be a issue getting a house like this to meet building regulations?

 

It looks like a huge saving in foundation cost. 

 

A steel portal frame would cost less than my quotes for feature trusses.

 

https://nacsba.org.uk/wp-content/uploads/2013/10/images_shoestring_18_shoestring13_ed-green.pdf

14043AFC-1EDD-4A81-9357-5956C9EE29D3.png

540B5C7C-7D1E-4179-AFAA-2C88165E6D73.png

55AFEBFB-CF96-497F-822A-C9970D970690.png

Great idea and all very doable. They make fantastic spaces / volume at a realistic cost.

Couple of points or so. A steel portal frame is a different animal from standard domestic construction. They tend to sway about more. When the wind blows on the side of the building it sways sideways. When you get heavy snow the roof flexes downwards. This is called horizontal and vertical deflection respectively.

Very generally on an agricultural type portal frame the limits Engineers set on deflection are slacker than those used when you have finishes on the inside that are attached to the frame or brickwork say on the outside. Some cladding manufactures also specify deflection limits for cladding as if the structural frame bends too much it over stresses the cladding fixings, your roof leaks and voids the warranty on the cladding.

For example on an agricultural building with a column height of 5.0m you could set a limit of column height / 100 = 50mm allowable sway under the design loads.

If you have a house you probably want to reduce this to below column height /300  or column height/ 500 which is ~ 10 – 16mm. Much better for your internal finishes.  If you are having one end as a barn (agricultural use and the other end as a house then you either need to decouple the two or maybe consider designing it all for the more onerous deflection limits.

If you are comparing prices for portal frames always ask what deflection limits the frame is designed to. Legally all frames need to be safe (not fall down and kill people / animals)  but the deflection limits are more flexible. If you ask for this information you can compare apples with apples in terms of cost.

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Just came across this kingspan case study using insulated sandwich panels on a French house, which I'm pretty sure is the first use of them on a purpose-built detached single dwelling I've ever seen

https://www.kingspan.com/gb/en-gb/products/architectural-facade-systems/case-studies/maison-if

 

Visually I'm sure it's not to everyone's taste, but a bold choice. Intersting that kingspan seem to be marketing it, suggesting they see potential in the residential market.

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58 minutes ago, kxi said:

Just came across this kingspan case study using insulated sandwich panels on a French house, which I'm pretty sure is the first use of them on a purpose-built detached single dwelling I've ever seen

https://www.kingspan.com/gb/en-gb/products/architectural-facade-systems/case-studies/maison-if

 

Visually I'm sure it's not to everyone's taste, but a bold choice. Intersting that kingspan seem to be marketing it, suggesting they see potential in the residential market.

 

Looks like the back diesel generator installation on a large industrial site. 

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10 hours ago, kxi said:

Visually I'm sure it's not to everyone's taste, but a bold choice. Intersting that kingspan seem to be marketing it, suggesting they see potential in the residential market.

Difficult to find something that is to everyones taste, but I like it and find it a lot more interesting than the neighbouring house.

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@kxi 

 

Thinking about using a steel portal frame for my build. I see you mentioned thermal brakes to prevent heat transfer into the steel within the building. Have you got as far as getting a price quote for the thermal brakes. Trying to get a cost per column for my costings sheet. Cheers 

 

 

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On 28/08/2020 at 23:15, gavztheouch said:

@kxi 

 

Thinking about using a steel portal frame for my build. I see you mentioned thermal brakes to prevent heat transfer into the steel within the building. Have you got as far as getting a price quote for the thermal brakes. Trying to get a cost per column for my costings sheet. Cheers 

 

 

 

Hello, only just got initial costing for these. Expensive. Estimated price is £7,000 for about 24 x 50mm thick armatherm FRR pads. So £350 per pad. Seems *quite* a lot. This was an estimated price from the steel frame supplier. Our building is unusual in that it has so many, so would be less of a cost in something more a normal shape.

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29 minutes ago, kxi said:

Hello, only just got initial costing for these. Expensive. Estimated price is £7,000 for about 24 x 50mm thick armatherm FRR pads. So £350 per pad. Seems *quite* a lot. This was an estimated price from the steel frame supplier. Our building is unusual in that it has so many, so would be less of a cost in something more a normal shape.

 

That is expensive, i was looking at the Armatherm 500 product for the thermal break in a concrete block wall, and got a direct quote from Armadillo (01274 591115) yesterday for 100m length total.

 

2000mm x 100mm x 50mm Blanks of  500-160 - £20 per unit + VAT

2000mm x 100mm x 50mm Blanks of  500-250 - £30 per unit + VAT

 

I can't see how 50mm FRR pads is that much more expensive, i would contact Armadillo directly

Edited by Moonshine
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