Ventilation with a Tin Roof

[mysticokra]

We have a 90 year old farm house in which the front section was originally a story and a half. When they finished it out it appears that they just screwed the sheetrock to rafters and left a small space between the ceiling and the crown of the roof. We get a pretty good heat build up when the sun shines on it. Since there don't appear to be any soffit vents or really ventilation of any kind, what would be the best way to relieve some of that heat?

I have thought about putting in a powered roof vent, but I don't know if tin roofs present any special issues.

Thanks.

[herbenus]

I'd consider putting in a lowered ceiling if you have the space. Then insulate, soffits, and vents. Other options:
1. remove ceiling, stick insulation in, replace ceiling, use soffits if you can.
2. nail an insulation board directly to ceiling, then new ceiling board. (I don't like this one.)
3. consider a suspended ceiling, with insulation. (I've no experience with these.)

As you can see I'm a believer in insulation and you seldom have too much. But everything should also be sealed and attics vented. I have the radiant barrier (foil) in my attic. I've always wondered if these offer any benefit with metal roofs.

[mysticokra]

I guess I should have included a picture for a frame of reference.

[Pat]

mysticokra, The heat you deal with comes from within and without. Your trying to deal with the outside heat that is getting in. Heat can transfer by three methods: convection, conduction, and radiation. Heat energy flows from the hotter object to the cooler ones by all three methods. By allowing convection currents under the roof, outside air will flow in under the eves and exit at a higher location that you provide (gable end vents, ridge vents, or ...) These natural convection currents will be driven by the heating effect of the sun on your roof and will remove a considerable amount of heat. A radiant barrier between the roof and the ceiling can reject a high percentage of the heat load that is radiated from the hot roof to the ceiling. Fiberglass batting and the like aren't the best for stopping radiant heat (they are for reducing conduction).

If you open up a considerable area under your eaves (covered with good anti-insect screening) and instal either a ridge vent or gable end vents for exit ports, that will help and is essentially a fixed one time cost. Fans just keep costing and costing but can be useful in some situations where you can't get enough natural ventilaltion.

Given your climate, you probably don't get a large temp drop at night in the summer. If this is true, the overnight whole house fan approach wouldn't do much for you.

Good ventilation of the attic reduces attic temps which in turn reduces the heat load on our ceilings. A good thing to do would be to place a radiant barrier below the roof with adequate ventilation between it and the roof. I have used rigid foam board with an aluminum coating on one side in a similar application. I left 2-2 1/2 inches of air space above the aluminum side to the roof. The space above the insulation board was open to the soffit vents and to the gable end vents. I placed F/G batts sized for 2x6 cavities under the foam board and drywall goes immediately below the F/G.

For those of you who were adding up the dimensions: 2 inches or so of air space, foam board (3/4 inch), and batts for 5 1/2 inches, you got about 8 inches. As the roof was decked on 2x6 lumber I had to fir down the 2x6 boards in the ceiling to get the required space. I ended up with about 9 inch or so cavity depth so as to not compress the F/G batts.

This installation was on about a 4 pitch south facing roof about 14ft (N-S) by 33ft (E-W). My goal was to make this enclosed porch (virtually all glass on three sides) usable in summer, i.e. not get much heat gain through the roof. All the windows can be opened to make the inside just about like the outside but much radiant heat from the ceiling could make the porch an uncomfortable oven instead of a nice shade.

There seems to be a lot of similarity in this project to your project. You have significant conductive and radiative heat loads. You need a radiant barrier AND ceiling insulation. If you can access the space you need to get some insulation in there AND a radiant barrier.

If all the space you have is the cavity between the ceiling sheetrock and the metal roof then you could remove the sheetrock and extend your rafters/joists (boards the sheet rock was hanging on and supporting the roofing.) By enlarging that cavity yo make room for a ventilation space (at least 2 inches), a radiant barrier, and insulation. Sheetrock is then hung on the now extended boards. This preserves as much ceiling height as is practical.

One really easy way to extend the joists/rafters is to screw metal studs onto the edges of the existing boards using drywall screws. This quickly and easily enlarges the cavities to allow for ventilation space, radiant barrier, and insulation. New drywall is attached to these studs (joists/rafters?)

Good ventilation and insulation + radiant barrier will make a real big improvement in comfort on hot sunny days and even make cool winter days more comfortable.

I have some kin in Mississippi and Alabama and have many fond memories of summer visits to their farms. I recall a great aunt's house with its tall ceilings and space under the floors to walk upright (I was young and under 6 ft then). There was a fireplace in every room except the kitchen (it had a wood burning range). I recall the really looooong handled brooms used to sweep the ceilings.

Best of luck to you. Let us know what you do and how it works.

Patrick

[mysticokra]

Thanks for the help. I suspect I will tackle the power venting first. I would rather go to the dentist that replace sheetrock. [img]/forums/images/icons/grin.gif[/img]

[MarkV]

</font><blockquote><font class="small">In reply to:</font><hr />
I would rather go to the dentist that replace sheetrock.

[/ QUOTE ]

That is a mighty close call. [img]/forums/images/icons/grin.gif[/img]

MarkV

[diamond]

I would go with the powered vent first,and see what the outcome is

[Bird]

The powered vents may be a good idea, but when I bought a new house in 1977, I talked to the local fire marshall about vents and he told me that he had no proof, but they had long suspected that many fires that start in the attic were caused by the power roof vents; usually not checked or serviced, owners don't even know when they quit working, wiring that deteriorated, etc. Like I said, he had no real evidence; only suspicions, but anyway, I installed wind turbines instead.