Class Q - Steel portal barn conversion cost estimates

[Stoph43]

HI all, very new to the site but i've been digging through lots if really useful information in this forum.

 

Quick question for those out there that have gone down the Class Q route, which many have already completed.  I'm looking to get some early estimates for a barn conversion. Its a typical 3 bay steel frame barn, reasonable concrete floor approx 200mm thick. Barn is 10.3m wide by 13.5m long, ridge height of 4.5m, It will be mainly 1 storey,  with the exception of mezzanines for the bedrooms.

 

Would be great to get an idea on what costs you guys have spent on similar barn conversions.

 

I have lots of other questions but we'll start here for now 😉

 

Thanks in advance guys 

[saveasteading]

I haven't, but i have previuosly declined any involvement in such a project, where the existing structure was falling apart but had to be retained. Thus the structure had a high negative value, but the budget didn't allow.

Have also looked at some for ourselves and either walked or been beaten on our offer....knowing too much.

Some more info,  maybe photos, of yours would be a help to being more positive.

Sticking to single storey is a plus.

Wall rails and purlins steel? Cladding? Your intended layout and cladding.

 

In theory a barn can not be lived in without strenghtening and underpinning , as there are no safety factors. There are solutions, some not too expensive.

 

Cost is much the same as a new build, maybe less, probably more.

[Tom]

Knock it down and start again? Probably cheaper, and the finished building would no doubt be better. A good few on here (including me) have had full planning granted for a new build once the change of use under Class Q has been confirmed. Easier to get that than it was for the Class Q TBH.

[saveasteading]

Maybe just my location (SE), but the existing building has to stay, or planning is lost.

[Tom]

34 minutes ago, saveasteading said:

Maybe just my location (SE), but the existing building has to stay, or planning is lost.

Which is why you apply for full planning permission. Then you can knock the buiulding down with gay abandon

[Stoph43]

@Tom thanks for the reply, this is very interesting and something we haven't looked hard into, as already know our local council are really tight in the class Q rules, and have been tools that getting full planning after permitted development is even trickier, but as you say it seems the most sensible solution form a build efficiency aspect and product performance out look.

 

Out of interest how different was your build form the class Q approved building to what you actually build? foot print, height, layout etc etc, and your overall costs would also be of interest if possible

 

Thanks again

[Stoph43]

@saveasteading,

Thanks also for your reply

 

 

Please see very rough image below, but you can see the roof and wall construction. Its has wooden purlins for both wall and roof, We plan to keep with steel cladding for both walls and roof (obviously insulated) build method is undecided yet as i'd really like to minimise the floor space loss but trying to work out the best solution of overcoming the cold bridge through the steel uprights, not building outside of the current floor print (class Q restriction) so still undecided. Layout is very simple also see below: What makes you think we'd need to underpin the steel uprights? i though this maybe this case, but am getting mixed opinions.

 

Thanks again for your response

 

 

[Mr Punter]

Did you just rent the sheep to get the class q?

[Stoph43]

 Mr Punter, I wasn't aware you could do this, is this a service you provide? Do you have any information on the question I have asked?

 

Thanks

[IanR]

Hi @Stoph43 and welcome.

 

I'm now living in Class Q conversion that I got Approval for 6 or 7 years ago.

 

My Approval was in the early days of what was then Class MB and there were no Appeals to get a wider legal opinion on the interpretation of the rules. My LPA wouldn't accept the Class Q Approval being material to a full planning application for a knock down and re-build. There are now Appeals and case law that say a Class Q Approval should be taken into account when considering the merits of a full planning app.

 

If I did mine again, that's exactly what I'd do. The existing steel structure compromises the Engineering of the conversion and the compromises either need to be accepted or you need to spend money to resolve them. I chose the latter, and am very happy with the result, but it would have been cheaper to do a comparable new build.

 

This is not a reason to walk away from a Class Q though,  the compromises should be priced in to the value of the plot.

 

Costs will be dependant on your aspirations for building performance, levels for finish and site related costs for Services hard landscaping etc.. It's not likely to be less that £2K/m², but could be more than £3.5K/m², unless you plan to do a lot of work yourself.

 

I'd suggest you speak with an SE sooner rather than later. The existing structure is unlikely to take the loads of a habitable mezzanine, and possibly not the framing to hold the insulation. Yes there are insulated profile cladding options, but think carefully about these and how you would use them without exceeding the existing buildings dimensions, achieve reasonable air-tightness and mitigate the thermal bridging of the existing frame.

Edited November 23, 2022 by IanR

[Tosh]

33 minutes ago, IanR said:

Costs will be dependant on your aspirations for building performance, levels for finish and site related costs for Services hard landscaping etc.. It's not likely to be less that £2K/m², but could be more than £3.5K/m², unless you plan to do a lot of work yourself.

I would agree with these figures for your budget needed. I think I'll come in slightly lower than £2k/sqm but doing mountains of work myself to get near that figure. We had full planning to convert so not Class Q but still had to retain the steel portal frame. You can almost be certain that the steel frame will be of no use whatsoever structurally hence do your best to get permission to take it down. Then you should be back into some sensible cost/sqm figures as effectively a new build. As I said we couldn't so had to tie new foundations into the existing pads, work out a construction strategy to work with the steel frame etc etc. Been a right pita for absolutely no benefit other than to meet a planners policy. 

[saveasteading]

1 hour ago, IanR said:

existing structure is unlikely to take the loads of a habitable mezzanine,

Or of the structure itself.

The problem first, then the solution.

Farm buildings have no safety factor. Occupied buildings of course have a factor to allow for freak weather,  bad workmanship etc., with people being valued above tractors or animals.

Therefore I can promise you that the farmer who built this did not put in, of pay for,  any more concrete or steel than necessary. Therefore the steel and foundations will not be sufficient for a house. 

Enlarging the foundations and strengthening the frame is expensive. 

The answer is to find a good and pragmatic SE who can find alternatives. 

For example, building an additional steel column for each portal frame, on a new foundation  internally is very much cheaper than attengthening what is there. They can be on the lines of new internal walls.

 

As to insulation. If the steel structure is completely contained within your new insulated envelope, then that is best. 

There will be some heat loss through the steel into the foundations, but not a lot. A subject for later.

[Tom]

20 hours ago, Stoph43 said:

@Tom thanks for the reply, this is very interesting and something we haven't looked hard into, as already know our local council are really tight in the class Q rules, and have been tools that getting full planning after permitted development is even trickier, but as you say it seems the most sensible solution form a build efficiency aspect and product performance out look.

 

Out of interest how different was your build form the class Q approved building to what you actually build? foot print, height, layout etc etc, and your overall costs would also be of interest if possible

 

Thanks again

 

There was very little difference in the appearance of the building we applied for full planning for, save for the addition of more glazing. There is one similar case near us actually where they were given full planning for a very different structure and even on a different area of the plot. Once the principle of a residential buiulding being on the plot has been established under Part Q there's no reason really why you can't do the same and submit a different design, but as ever can very much depend on how your LA treats these applications. Worth a trawl through the portal to see if there have been similar applications local to you.

[Stoph43]

This is all really useful information thanks guys. Looks like i'm going to have to pump a lot more money into the foundations ad structure as i first thought. I will see how we get on with the pre-app and then probably take all of your advise in getting full planning as to make teh job a bit easier. To be honest we don't really want anything different, another 1000mm of roof height would be lovely but i don't want to push it.

 

My main focus was the structure (mainly for costings and design method) and how to incorporate the steel portals within the structure to minimise the thermal bridge. SIPS on the inside of the steel uprights seems the most sensible, but it does dramatically reduce our already quite small footprint. I did wonder if i could use ICF blocks to straddle the steel uprights, but then i'd probably be in danger of going outside the overall dimensions.

 

What has been your guys chosen build structure method?

 

Thanks

[saveasteading]

2 hours ago, Stoph43 said:

SIPS on the inside of the steel uprights seems the most sensible, but 

But the columns are exposed and need very high quality painting.

Sips outside on the roof, so why not on the walls too?

 

I've done lots of steel buildings mostly new, some reclad. I've only left columns outside when there was a need for flush internal walls. It is more complex , especially in getting an airtight insulated joint at the haunch  (interface to the rafter). Looks better though.

[IanR]

36 minutes ago, saveasteading said:

Sips outside on the roof, so why not on the walls too?

 

If the conversion is completed under Class Q then the converted building can not extend beyond the original building, so if the portal frame is visible on the outside there is no opportunity to enclose the frame within the thermal envelope. If it's not converted under Class Q, then it's best to avoid keeping the portal frame.

 

3 hours ago, Stoph43 said:

how to incorporate the steel portals within the structure to minimise the thermal bridge.

 

Your drawings show the portal frame to be aligned with the external surface of the external walls of the original building. Under Class Q it would be best to leave these entirely outside the thermal envelope and avoid any thermal bridge. Since the uprights connect to the primary roof structure, I'd also leave the roof beams and purlins outside the thermal envelope, as steel has exceptionally good thermal conductivity.

 

3 hours ago, Stoph43 said:

Looks like i'm going to have to pump a lot more money into the foundations ad structure as i first thought.

~~~~~

What has been your guys chosen build structure method?

 

In order to not have the building performance compromised by the steel portal frame, I built an I-Joist timber structure (walls & roof) within the portal frame, dovetailing the timber structure around the steel structure, but not letting them touch. The Steel portal frame is still in place, including the roof portals and Z Purlins, which continue to hold up the light weight rains screen, which in my case is a standing seam metal roof. The timber structure supports the 300mm - 350mm blown cellulose fibre insulation in the walls and roof, as well as the mezzanine.

 

The internal columns of the portal frame took some careful detailing to keep those outside the thermal envelope.

 

You asked on PM for some more details on my conversion, so just in case you've not found these posts previously, I'll add them here. Fell free to ask any questions if something is not clear.

 

 

 

 

[gc100]

I finished my class Q build nearly 2 years ago. We actually went for full

planning after the initial class Q was granted as we wanted to extend the length/size. However it all had to go to committee to get it through as we have had all out PM stripped pretty much and had to stick to the original footprint and existing structure. It was in a right old state but we had an excellent structural engineer who came up with a clever design. We have a pretty high quality build (air tight, triple glazed, zinc roof, clad) and total all in was 2.9k/m including all the paperwork, services etc. 

[LSB]

On 22/11/2022 at 17:30, saveasteading said:

Maybe just my location (SE), but the existing building has to stay, or planning is lost.

same for East Anglia, knock down counts as new building, in the country probably, big no no, so however much better a new build would be you convert or give up

[saveasteading]

On 02/12/2022 at 17:06, IanR said:

under Class Q then the converted building can not extend beyond the original building,

 

As there is wall cladding then that would define the available outer limit. so you have 20mm or more to play with, if anyone is measuring that closely.

 

But then what if you drop a string line from the edge of the roof  sheeting, does that give extra width?

 

Even if you could only squeeze in 20mm PIR outside the columns, that will do enough, and can be made up for in other ways (discuss later if this works in principle)

 

I do not agree for a moment that you should leave the rafters and purlins exposed, if that is what the above suggestion is. It would need heavy protection and would be , let's say, quirky. It works in the Mediterranean but not here.

 

Are the purlins  (pedantic corner here...purlins are only on the roof, the walls have wall rails (or girts  in American and some of Europe))

yes, are the purlins set on top of the rafters or inset?

 

What do you plan for the wall construction?

 

You will be stripping the wall and roof cladding. Has anyone already measured the existing dimensions?

 

This is all worth many thousands to you, so any more photos or sketches may be worthwhile.

 

[IanR]

2 hours ago, saveasteading said:

As there is wall cladding then that would define the available outer limit. 

 

I'm going by the drawing provided that shows the outside surface of the Portal frame level with outside surface of the wall. I had assumed the profile sheeting is just in the upper areas, a short distance down from the eaves, as is typical with agricultural portal frames.

 

Even if the profile sheeting went from eaves to floor, the 40mm that gives you, outside the portal frame is insufficient to stop a thermal bridge. You still need a rain screen on the outside of any insulation.

 

2 hours ago, saveasteading said:

But then what if you drop a string line from the edge of the roof  sheeting, does that give extra width?

 

The wording in Class Q is that you can't extend beyond the existing envelope at any point.

 

How I dealt with that was to have an upper cladding outside of the portal frame, in the same way the original profile sheeting was, but have the lower cladding inset, level with the portal frame, in the same position the original walls were, which means the portal frame is still visible externally at the lower level, as it was on the original building.

 

 

 

 

2 hours ago, LSB said:

same for East Anglia, knock down counts as new building, in the country probably, big no no, so however much better a new build would be you convert or give up

 

It is now recognised in the planning guidance that a Class Q Approval should be taken as material for a full planning. However that doesn't necessarily get you to a knock down and re-build. But it should at least allow the Class Q rule of not exceeding the existing building envelope at any point to be ignored, leading to the chance of brining the portal frame within the thermal envelope, and it should open up additional building works that are otherwise restricted by the Class Q.

Edited December 3, 2022 by IanR

[Tosh]

On 02/12/2022 at 12:54, Stoph43 said:

I did wonder if i could use ICF blocks to straddle the steel uprights,

Like this....

[HughF]

On 02/12/2022 at 12:54, Stoph43 said:

This is all really useful information thanks guys. Looks like i'm going to have to pump a lot more money into the foundations ad structure as i first thought. I will see how we get on with the pre-app and then probably take all of your advise in getting full planning as to make teh job a bit easier. To be honest we don't really want anything different, another 1000mm of roof height would be lovely but i don't want to push it.

 

My main focus was the structure (mainly for costings and design method) and how to incorporate the steel portals within the structure to minimise the thermal bridge. SIPS on the inside of the steel uprights seems the most sensible, but it does dramatically reduce our already quite small footprint. I did wonder if i could use ICF blocks to straddle the steel uprights, but then i'd probably be in danger of going outside the overall dimensions.

 

What has been your guys chosen build structure method?

 

Thanks

My builder friends are doing block/block, 200mm cavity, steels partly in the cavity. 

 

Don’t underestimate the steelwork involved with repairing the column bases - I’m a welder and me and my structural steelwork friend did a bunch of columns back last year, plating 150mm either side of the ‘zone of decay’. By the time we were halfway through the horrible job, we both agreed it would be quicker and far better to do a cut out and splice on the affected columns. 

Edited December 3, 2022 by HughF

[saveasteading]

16 hours ago, IanR said:

40mm that gives you, outside the portal frame is insufficient to stop a thermal bridge.

No, there is an easy enough way. Stoph43, I will deal with this for you if you wish to pursue this solution...but it is your project and your money.

[Dave Jones]

take the m2 cost for a standard build of the same size and double it. 

 

 

[Stoph43]

On 03/12/2022 at 21:16, Tosh said:

Like this....

@Tosh This is EXACTLY what i was thinking, haven't been able to find any examples of this but what you've done matches my thought process. I'm guessing you've had to apply for full planning approval for this rather than a class Q?  How di you finish the insides and outside of the ICF, it looks like a sensible construction method to be as you gain the thermal mass, structure and insulation without losing too much floor space which is critical in my build. Are you able to provide anymore photos. Happy to private message me if that helps. Great build!!!