DIY Stable Renovation: Need Your Advice and Ideas!

Section62

ThisIsWeird said:

Oops - I thought I was suggesting what you had recommended? Then just OSB and metal-sheet the roof as S62 suggested?

You are saying the upper roof needs insulating too, in addition to the OSB?! Lawdie.

Not "too" - it would be 'instead of'.  Move the (whole) insulating layer above the purlins and (1) it is easier to install and (2) it deals with the condensation issue and helps insulate the room below. (aka 'warm roof')

ThisIsWeird said:

Ok, this is my final offer, and then I'm shutting up... I would Tyvek over the rafters, horizontal batten as if fitting a slate/tile roof (except at spacings that the sheeting co recommends - say 2'?), and then screw the metal sheets to that. Ensure the roof void is well insulated. Jobbie jobbed.

If that doesn't do the trick, the world's gorn mad.

That doesn't address the steel condensation issue.  The Tyvek will sag between the rafters and the condensation dripping off the steel will pool on top of the Tyvek. With a steeply-pitched roof the water will reliably run down the Tyvek and into the gutter, but with a shallower pitch that sujsuj has on the stable the membrane needs to be supported so there is a constant fall down the roof slope.

It also sounds like far more work and effort than simply covering the purlins with a sandwich of OSB/Insulation/poly/steel.  Cutting and fitting all those battens (not to mention the cost) is unnecessary hassle.

The only reason not to put the insulation above the purlins is if that would take the overall (or eaves) height over those allowed for permitted development - but in this case I don't think sujsuj needs to be unduly concerned about that.

ThisIsWeird

I would only add insulation to that setup if I was going for a vaulted ceiling.

Tyvek might sag? Surely no more than it does in any roof? It seems to work fine in my garage, with a slate roof - which gets bludy cold. No visible condie.

sujsuj

What about using Tyvek Housewrap Breather Membrane instead of celotex to avoid condensation and adding more insulation (celotex) covered with plaster board inside?? I am worried about working on too many thick layering while on the roof!

(1) Outermost corrugated metal sheets
(2) Polythene membrane  
[3] Tyvek Housewrap Breather Membrane 

[4] OSB3 Board
===============================
(5) Celotex/ similar cut b/n rafters (inside)
(6) Thin Plaster board (inside)

FreeBear

sujsuj said: (5) Celotex/ similar cut b/n rafters (inside)

Have a look at GapoTape (similar products available) if you are using thick sheets of insulation. It is an adhesive foil tape with a strip of foam down the middle that you stick to the edges of the insulation boards. When pushed in between the rafters, it fills the small gaps left when cutting boards. Supposedly cuts down on cold spots and reduces warm moist air getting to the cold side.

I'm with @Section62 on having a layer of insulation between the steel roofing sheet & OSB. Absolutely no point in having a breathable membrane directly under a sheet of plastic.

Section62

ThisIsWeird said:

I would only add insulation to that setup if I was going for a vaulted ceiling.

sujsuj has said from the first post he wants to add insulation to be able to use the space for 'domestic' type activities such as a home gym.  If he's made the decision to insulate then the only question is where best to put the insulation - in other words whether to go for a 'cold roof' type arrangement, or a 'warm roof' type arrangement.

For all the reasons I've given at length in the thread so far, emulating the 'warm roof' approach is better in this case primarily because of the metal sheets he intends to use for the roof.

ThisIsWeird said:

Tyvek might sag? Surely no more than it does in any roof?

As I said in the previous post, not really an issue if the roof is steeply pitched, but with a reduced pitch you can get ponding, and that has to be avoided at all costs.  One way of avoiding sagging (and therefore ponding) is to lay it over the top of something solid and flat - like OSB3 - which brings this discussion full circle.  Don't take my word for it, check the Tyvek technical documentation if you wish.

ThisIsWeird said:

It seems to work fine in my garage, with a slate roof - which gets bludy cold. No visible condie.

Slate is a different material to sheet metal.  A slate roof will have a higher thermal mass and lower thermal conductivity - it is less prone to condensation forming.  Furthermore, it doesn't corrode like steel if condensation does form.  And the surface of slate is slightly porous meaning mild condensation will remain attached to the slate surface rather than dripping off.  The surface of slate works in a similar way that drip-stop fabric would - holding the condensation and then allowing it to evaporate away when atmospheric conditions allow.

The fundamental point (which it feels is not fully understood) is that metal (including steel) sheet roofing has specific characteristics that you don't get with other roofing materials.  If you use metal sheeting for roofing then you need to design the roof to manage the condensation issue, not design the roof as if you were covering it with slate, or anything else.

Section62

sujsuj said:

...I am worried about working on too many thick layering while on the roof!...

You are worrying about the wrong thing.  Building the thickness of the roof up with multiple layers will make it stronger and safer to walk on the end result.

Safety comes about by following a safe method of working - there are lots of things you'll need to do to be safe while working on the top of the roof, one of which is only walking on things that are securely fixed, and another is only stepping on things that have the capacity to bear your weight.

So long as you adopt a safe method of working, working on the roof should expose you to less overall risk than a method of working which involves trying to fit cut sheets of celotex between the purlins from underneath whilst standing on a ladder.  This is one of the reasons why I suggested you first cover the roof with OSB of a thickness that can support your weight, then build the roof up in layers which will help to spread the load.  Then the primary thing you have to worry about is working in proximity to the periphery of the roof (i.e. falling off the edge).

If you don't feel comfortable or safe working at height then get someone in to do the job for you. Safety is paramount and it is impossible to install a sheet metal roof without having to stand/walk on it at some point.

FreeBear

Section62 said: So long as you adopt a safe method of working, working on the roof should expose you to less overall risk than a method of working which involves trying to fit cut sheets of celotex between the purlins from underneath whilst standing on a ladder.

Having boarded a ceiling with 6x3 sheets of plasterboard using step ladders on my own, never again. A scaffold tower has made the job a lot easier and safer - Still use 6x3 sheets, as 8x4 sheets are just too heavy for me to handle.

sujsuj

I managed to get all the metal sheets dried today. Need to wipe clean other side!

sujsuj

I did a trial run by placing the metal sheets over the existing roof. There are many questions and a lot to learn before starting the actual work. See photos attached.

sujsuj

1. It seems I’ll need to cut at least one foot from the metal sheets, likely because they were closest to the nearest standard size (see Pic-2). I suppose it wouldn’t be advisable to to leave the sheet as is without gutter!!

2. The edge trim might need to be bent to match the shape of the sheet before securing it to the top (see Pic-6). Edge trims are thin hopefully while scewing I can force it into the shape.

3. "I’ll need to figure out how to manage rainwater runoff through the edge trim (see Pic-3).

4. Need to try out how metal sheets for sides and back will look

Any additional thoughts?