Insulating a roof with no attic space


Old 08-12-09, 03:46 PM
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Join Date: Aug 2001
Location: USA
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Insulating a roof with no attic space

I have restored an historic building and am now running it as a B&B. I've weatherproofed and insulated it as well as I could but there is one room that is giving me real headaches.

The upstairs room of the kitchen building was built with no attic per se - just whatever space that was created between the ceiling joists and the roof, so the Texas sun comes screaming through it.

The roof is flat metal with a slight incline. Pictures here and here.

Right now my plan is to put down an elastomeric white paint to reflect some of the heat, but I'm wondering if this is a good idea and if there is anything else I can do.

Since it's an historic building (National Register and all) I'm always reluctant to make major modifications, but right now the room is almost useless during the summer months, so I'm open to all ideas.
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Old 08-12-09, 06:55 PM
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Join Date: Feb 2006
Location: Williamsport
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Is there any access at all to the space above?? If not, this is a long shot, but what if you blow in cellulose insulation in between each joist?? It looks like a metal roof, does it need to have ventilation?? Just some other questions and thoughts? Hopefully someone professionally comes along for ya!
Old 08-13-09, 06:13 AM
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Join Date: Aug 2001
Location: USA
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There is no easy access to the space. From below you'd have to cut away sheetrock and remove some of the ceiling planks, and from above you'd have to peel back some of the metal roof.

Ventilation? There's no ventilation at all. It's a solid brick building, so to get to the space from the side you'd have to work your way through 3 or 4 wythes of bricks.

Hmmm... OK, now I'm just thinking out loud while I wait for the experts to show up.

What if I removed about 6 inches along the length of the metal roof at the top, covered the hole with a screen, and built a mini roof for the hole with flashing? Basically I'd be creating a ridge vent. Even then I'd still need vent holes at the other end to create the air flow. OK, that approach doesn't look promising.
Old 08-13-09, 06:43 AM
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A non-vented roof is called a "hot roof". You would fill each rafter cavity with insulation and seal it up. I'm not a fan of hot roofs, but in many situations they are the best option. Here are some risks. If you ac, then the inside of the building will be cold enough to condense moisture from hot humid outside air. The insulation and air sealing must be such that the outside air does not reach a cold/cool surface. Also, once you fill the cavity, any moisture that gets in there will have difficulty escaping.

I'm from the north so not that familiar with flat roofs such as yours. I would suggest talking to a couple of spray foam companies to see what they suggest.

An approach I have used is to cover the ceiling with a couple of inches of rigid foam and they a layer of sheetrock. Not sure if that is an option for you.

Old 08-13-09, 07:06 AM
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There are companies here in Texas, may have to check Houston or Dallas for one, that spray metal roofs with foam then spray the whole thing with several coatings of a flexible sealant. Given the condition of your roof it looks like it could use such a treatment to be sure it doesn't rust through.
Old 08-13-09, 01:49 PM
Join Date: Nov 2001
Location: USA
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The parapet will allow you to build up the roof. Lay 3 inch foam board insulation on top of the metal roof, tape seams and lay another 3 inches of foam board insulation on top of the first layer and tape seams. Lay 1/2 inch plywood (roof sheathing rated) over insulation and secure with minimum 7 inch screws and lay water proof membrane (light colored) over plywood. Any decent roofer will know how to deal with the roof drainage.
Old 08-13-09, 02:21 PM
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Join Date: Aug 2001
Location: USA
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The roof is actually in pretty good shape. The rust you see is superficial and the only problem areas are where the metal roof meets the brick parapets, but even that's been patched pretty well.

Unless someone tells me otherwise I'm not seeing a big downside in applying the elastomeric paint. If that doesn't make the situation at least tolerable, then I'll have to look at somehow getting to the rafter cavities and adding insulation to the ceiling.

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