Insulation under slate

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Author Message   JIM Posted on Monday, February 23, 2004 - 09:23 am:        Is this a problem? My neighbor is installing fiberglass insulation directly to the 1 by sheating under a slate roof on a 1800's house. As there is no ventilation system, what is the possibility of causing a problem? The home is in northeast Ohio. Thanks.   Joe Jenkins (Admin) Posted on Monday, February 23, 2004 - 11:22 am:        Best to leave an air space between the insulation and the wood and critical to have a vapor barrier (sheet of plastic for example) INTERIOR to the insulation, otherwise warm air can infiltrate into that cold air space and condense moisture.   Dominic Meehan Posted on Thursday, October 21, 2004 - 12:47 pm:        I am about to have the underside of my slates sprayed for insulation, however I have received conflicting reports on it effectiveness.(One source has told me it may dislodge slate and will reduce ventilation in the attic space. Another source has told me it is an excellent job for an older roof but is very messey in the event that the roof may need work/renovation in the future.)The house is 1950's and there is no felt on the slates, could you please advise me and give me the pros and cons? Dom.   Peter Posted on Thursday, October 21, 2004 - 03:50 pm:        Hi Dom, The one major problem with that type of system is it stops all air from venting the roof space, that can cause the main timbers to rot. A lot of UK local authorities were very excited about system in the 1980's, the reports back today are all in the negative. Any roof being sprayed needs to be in very good condition because repairs can be very difficult after the sprayed foam is in place. If there are any leaks water can soak into the foam, wet foam has zero insulation value and can help the rot process in the main timbers. There are different types of foam some can absorb moisture others can't so the water travels down the top and dislodges the foam off the slates. Irish Building Regulations are very strict about a two inch space between the insulation and the roof covering. Problems have been known to occur because the warm side (attic) meets the cold (against the slate) and causes condensation in the middle of the sprayed insulation. Perhaps you insulate at the ceiling level and keep the heat inside your home where it will be most effective. Regards, Peter Crawley, M.I.o.R. www.crawleyroofing.com