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Question DetailsAsked on 10/1/2016

getting condensation on metal ceiling of a low sloping roof with no insulation

Sunroom has a aluminum plank looking ceiling, condensation forms on ceiling and freezes over in Winter, roof has no insulation, roof has ridges about a foot apart and are about 3" high. Need to cover roof with some type of insulation. Will polyiso panels work on top of roof and if does it have to be covered with something. Thanks

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1 Answer


Here is a previous similar questions with response FYI -

Generally speaking, with raised seam roof like you have, insulation over the top does not go well - both because insulation over metal roofing, while done as exposed insulation in industrial applications (like on tanks, but it is coated with a protective urethane or other coating), does not fit well or look good on residential jobs. The right place for it would be under the roofing - meaning taking off roofing (may or may not be able to easily do that depending on your - but you cannot by code have (and do not want) exposed insulation in the ceiling of the sunroom either, so sheathing (plywood - and usually use marine plywood if sunroom is not included in the house's "conditioned space" or is not heated in winter) would have to be placed over the rafters or purlins (if not there already), then insulation board, then underlayment (water barrier), then the roofing. And of course on the underside of the roof you would presumably want some architectural treatment for appearance sake but not a water / vapor barrier. Sometimes tongue-and-groove sheathing is used so the underside is presentable from the inside, if you have exposed rafters/roof trusses.

Only other solution thst is easy, but expensive - make it a hot roof - keep underside of the roof well above freezing (actually probably above about 45-50 degrees to prevent condensation) and improve air circulation to prevent condensation. And use dehumidifier to keep cool/cold weather humidity down, though that can irritate some people and cause wood surfaces to crack.

One other possibility - could be minor leakage is coming through roof and condensing/freezing on the underside - look for signs of drips or thicker or more clesar icing, rather than jsut frost from condensation from the air.

Architect would be the person to best address what you can do and rough costs of alternatives, but I strongly suspect the recommendation will be either remove the standing seam roofing and put down sheathing, board insulation, and replace the roof - or do same but replace roof with a membrane roof, which would be the more normal roofing type for a low-slope roof.

Answered 3 years ago by LCD

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