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Steel Barn conversion - metal composite roof


jen and mark

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Good morning,

 

We are in the process of converting a double steel portal barn and are considering having a steel composite roof to u value 0.15. As I see it, the pros would be:

  • Complete roof - quick to install
  • No thermal break - the steels would be inside the thermal envelope
  • We could expose the steel purlins in our vaulted roof - giving a nod to its agricultural heritage

cons:

  • Condensation - condensation on the steel frame, and possibly forming within the walls.

 

So my question is has anyone ever used these composite steel roofing panels as the final finish internally?

 

The construction is.....

We have raised the  original floor by approx. 420mm - usual hardcore (MOT type 1), blinding and DPM - Gen 3 with fibres being poured on 23rd August. This meant we did not have to dig out the already solid base. We have a single skin block wall ( about 4ft high) between the steels which we will add a timber stud on top and then add a second timber stud wall, internally, to create a cavity, we will insulate (to building regs) the 2nd stud wall. The outside will then be clad with a combination of steel and wood cladding with nominal insulation to avoid heat losses through the steel frame.

 

We will always have a problem with cold bridging from the floor as the steel stanchions have no thermal break on the pads. Our plan is to wrap the bottoms of the columns in Celotex, where they came through the floor, to thermally break them from the insulated slab, that includes the UFH. A tip given by @IanR.

 

Any help would be appreciated!

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  • 9 months later...

How did you decide on doing the insulation in the end? I've seen your other posts saying the roof is on, but couldn't find reference to what you did. I'm just starting out on one, and was hoping to site the insulation between rafters with just a strip on the lower face that would have been exposed. 

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We've using 150mm thick steel composite panels for our roof, hopefully finishing it this week. Then planned an additional 200mm layer of wool or cellulose underneath these/between the purlins. U value should be <0.10, but of course the devil is in the detail

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We went for QuadCore KS1000RW Roof Panels thickness 137mm to give a u value 0.13W/m.K. https://www.kingspan.com/gb/en-gb/products/insulated-panel-systems/insulated-roof-panels/quadcore-ks1000rw-roof-panel 

 

This is our final finish - no plasterboard or additional insulation. We love it and it gives a nod to the industrial/agricultural steel barn that it used to be! Although the panels are not cheap it has saved us money on plastering! 

 

I will try and post a photo tomorrow so you can see!

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Forgot to say ... we have not had a blower test yet but the panels where well sealed as they were installed. Sound is a lot less than a poly carbonate conservatory roof when it rains which was a worry of mine 🤣

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Very cool! You are well on with it, looks great! But I presume the stanchions are outside the insulation on the perimeter of the build?

Are you going to leave the internal stanchions exposed, I guess no point in insulating them given the rafters are all exposed anyway.

 

Looks an amazing space!! Be transformed once screed is down!

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Cheers @daunker not to everybody's taste but we do have the option to plasterboard at a later date when we have more money - everything has doubled in price since we originally costed it out in Nov 2020! These things are something we can do anytime (though disruptive and messy). The main money has gone in the fabric of the build!

 

We had to think hard about the insulation, thermal bridging and condensation (and class Q restrictions) so we wrapped the external stanchions in sprayed on closed cell insulation with a small amount of exterior insulation over the complete outside shell and the remainder inside. The roof provides full exterior insulation so the rafters are inside. The inside stanchions will also be fully 'wrapped' in foam and insulation apart from 1 which will remain open. We will always have an issue with thermal breaks from the stanchions in the ground but as had plenty of head room, we built the floor up with plenty of insulation!  We got the idea from @IanR - see previous post that has some good photos of what he had done with his build. Hope this helps - we found it one of the most head scratching times in designing the barn as we have no architect. Everyone was telling us we would have condensation issues with no thermal breaks but our structural engineer and building inspector said that this would be very unlikely given what we have done and with the UFH and MVHR system - time will tell! What I have found is that compromise is the name of the game and as we hope to never leave, we are doing the best we can with the money we have - we are completely doing the work ourselves. Prior to this, we lived in an self build house built in 1963 so this has to be better!

 

We are currently on ECP of B - 85 so are hopeful our blower door test will bring this down even further!

 

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I like the look! It was just its a real panic of mine to have the internal/external crossover. So glad to hear doesn't seem to be so much of an issue. Did you manage to put much external insulation on them - I'm reckoning if in a block wall you could only get the outer face - not the internals of the I which would have been blocked right up to it? But reading your post again looks like you managed to get all the way round the steels - which is interesting. Yes I'm class q too - bit of a headache!!

 

Good idea on the central pillar -will be doing the same. I think I'm going to put insulation under the rafters but does mean losing height. Yours is looking fab - good luck!

 

The mvhr systems I've seen I thought required drop ceilings and ducts to all rooms - but your vaulted ceiling is exposed - am I missing a trick for how to do it?

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  • 3 weeks later...

Sorry just seen this - finally finished the screeding 😫🤪.

 

We have dropped ceilings (8ft high)) running through our study, pantry, utility, bathroom 2 so that covers roughly north to south. Others are going through central double studded wall and the remainder (mainly in spare bedroom across to back door) will be boxed in or left open - yet to decide. This provides ducts to all rooms. Really glad we went for properly designed plans for this (including commissioning). We went for  spiral steel ducting in the end so we could leave on show. Now it has all arrived I am not too sure where to begin! 😂

 

With regard to the insulation - we encased the 4ft concrete walls alongside the steels both inside and out so they are sandwiched in the middle if that makes sense (Slightly more on the inside due to class Q restraints). The roof is full external insulation. It was the best we could come up after many nights head scratching and asking for ideas through the forum!

Edited by jen and mark
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