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Restoration of a 150 year old Barn.

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sean_ork:
It's a little late now, but a multifoil negates the need for massive FG thickness and a separate VPL - there's a lot of roofs being ruined here by folks who think more is better (which to some extent is true) - but adding additional absorbent materials without due regard to correct positioning of the VPL will result in soggy insulation, and eventually a rotten roof.

Fortunately cold roofs are effectively banned here, no warrant will be issued if the design includes one.

dnix71:
When you mentioned "cold roofs" I had to look that up.

In America what you call a cold roof is common an acceptable in many places. Our lumber is pressure treated to prevent rot. What people need to be careful with a cold roof is enough ventilation to prevent water condensing above the insulation.

The second risk is if plumbing is placed in the attic. I lived in Chattanooga, Tennessee for a year in a row of "townhouse" style apartments. The second floor of each unit was open to the first in the front by a wrought iron spiral staircase and the water and sewer was included in the rent. The pipes ran across the attic and down to each unit. The year I lived there one day the outside temps fell to 14F (-10C) and the pipes froze and burst above an unoccupied apartment. That made a mess that was not easy to repair. If the unit had been occupied, there would have been enough heat rising from the unit to prevent freezing.

The heating was all electric (Tennessee Valley Authority / 4 cents a KWH). My electric bill was $10 a month average.

sean_ork:

--- Quote from: dnix71 on October 25, 2015, 11:42:57 AM ---What people need to be careful with a cold roof is enough ventilation to prevent water condensing above the insulation.




--- End quote ---

That's the point, in the situation as described the dew point is likely to be at varying points within the FG.

clockmanFRA:
All standard Construction timber here in France is pressure treated properly, with real insecticides and anti/rot fungal agents.

Thank goodness the health & safety brigade of the UK are kept well out of France.

Personally speaking sean_ork, your talking rot again.........

sean_ork:
CM, believe it or not, I'm trying to guide you away from making yet another potentially very costly mistake.

I will now leave it to others to further the point, and yes, I'm talking rot - but it'll be your roof timbers that rot.

Don't worry, you'll get plenty of warning; obviously you are free to ignore me, maybe Mrs CM will ensure you don't ignore the mould that will grow on your ceilings. You'll then find all of innermost FG to be saturated.

My point has nothing to do with H&S, its just simple building health and very basic building standards.

Good luck.

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