Roof design & keeping humidity low

[bluesofa]

I want some advice firstly regarding the pitch of a roof.

Considering building a small storage facility near the house for a couple of vehicles and load of my other stuff (furniture, etc) for long term storage.

Think the footprint will be about 5 meters x 25 meters and say 2.5 meters high. It will be enclosed using solid block walls and access via a couple of roller shutter doors to keep everything secure.

Is there an easy/best way concerning the roof design?

Initially I assumed it would be a pitched roof ( like an inverted “V” shape), but now I'm wondering if a single flat sloping roof would be better - or is there a good reason not to do this? I was thinking of those large corrugated roof panels, rather than tiles.

Secondly, any suggestions on how to keep the stored stuff cool/dry avoiding too much humidity?

I did look at the price of a dehumidifier, but they're not cheap for a large area and the running cost would to too expensive.

I considered a couple of overhead fans with an extractor fan near the roof, or am I barking up the wrong tree completely trying to keep my stuff dry this way?

[IMHO]

The most effective way to keep a room naturally cool in Thailand is to ventilate it when the ambient temperature is low, then insulate it when the ambient temperature rises.

In your case, this is going to be challenging as what you're proposing is a room that's continuously locked up. I'd suggest a design that:

1) Effectively ventilates the roof crawl space - the roof cavity is almost always hotter than ambient, so nothing to lose.

2) Effectively insulates the ceiling in the room

3) Effectively insulates all walls - paying particular attention to those that will catch direct sunlight

I would expect a properly ventilated and insulated "V" roof would provide a cooler room below than a flat roof.

I can't see how a ventilation fan in the room would reduce humidity, as the supply air still needs to come from outside, and if running continuously, that means it'll be sucking humid + hot air in as well.

Most better AC's have a "dry" (dehumidify) mode, which by virtue of that way AC's work also means a marginal amount of cooling as well - perhaps that's an option worth exploring?

[passingas]

Will this building attach to any other? If not, incorporate what is called a Dutch Gable design roof. It is basically a hip roof (overhang protection) with areas you can put gable louver vents in. Oreintate these for maximum breeze (north to south, as the monsoonal change, dictates). As these vents will be at the top, heated air will naturally raise to them. Then use the vented soffit material for the underside of the overhang. This will vent the heat your roof will collect everyday, more than any other design. Also use a color that will maximize heat reflection. As far as humidity goes...about the only way you can control that is by running a dehumidifier. Put it on a timer, and have it drain to the outside, as it will collect water. Good luck pg

[bluesofa]

Thanks for the replies.

Points arising:

I take the point about a “V” roof being cooler. I've since seen that some rotating roof vents are available, they look to be about 30cm diameter – would a couple of these be a good idea?

It seems like these are a much better idea than the extractor fans.

I can see no reason to have a ceiling, as the building is only for storage – or would the lack of a ceiling affect keeping it cool?. My assumption is that the hot air could then rise unimpeded into the roof, keeping the storage area below cooler.

The comment about the Dutch Gable design: Had to google it to discover the details. I don't know if it would add more to the construction cost, but I did notice you said this would be vented more than most other designs.

No, the building won't be attached to another one, it will be totally separate.

If I did run a humidifier on a timer, I'm just concerned if it would that be cost effective? The storage area is about 300 cubic meters, plus the roof area (as there would be no ceiling).

I take your point about using a colour to maximise heat reflection.