Worried about heat buildup in loft

[faralta]

I'm having a 32x64 - 12' ceiling pole building built shortly that will be used for boat and car storage and occasional fair weather tinkering. Metal sides, dark grey shingle roof, soffit and ridge vents, unheated with a full length loft 14x64 under the 8/12 pitch roof. Located in south-central Michigan. Question is... how warm will it get in the loft in the summer and can I manage that with an exhaust fan in one loft gable end with air flow from a 3x5 double hung on the other loft gable end? BTW, it will have OHD's on each gable end too which should provide added flow at floor level.

 

[maxpower_hd]

It's hard to say how warm it will get exactly but I know it will indeed get warm. I suggest adding a ridge vent (Cobra vent is one) when you put the roof on and I would also use light grey or white shingles instead of dark anything to help reflect heat.

 

[Cyberbear]

I live in So. Calif. and your present plan would no doubt be workable here, so I'm thinking for your area of the country you'll still be alright. If not, changes can always be added.

 

[matt_i]

The loft will get pretty warm (well over 100F) if left to natural convection in the summer. I have a similar setup but shorter length in my existing shop.

The forced airflow will help this. I'd say it will have to be a bigger fan, lets just throw out 1/2hp for somewhere to start, in order to keep cool. One of those "whole house fans" is going to be overkill but is an easy choice if you could find one. A $16 box fan I think will be inadequate.

The downside is that a lot of airflow thru the shop will change the humidity level inside...if it rains you pull in a lot of humidity. Somewhat easier if the opening between ground floor and loft is well sealed but its easy to ramp up humidity fast. It depends what you are doing inside, if its simple storage, that may not matter, if you have precision machine tools, not the best idea.

I just store things in the attic area that i don't think will be affected by the temp extremes as it will be very cold in winter also. Another good reason to seal up the penetration thru the floor as heat will leak out the ridge vent like a chimney in winter.

 

[faralta]

matt, i plan on the loft being used primarily for storage, but can't rule out that it may become a "cool" spot for my kids to hang out as well. Do you think two roof mounted power vents would be better than a sizable gable-end fan? I would think the objective is to create more draw than can be easily supplied though the soffit and eave vents since these will provide airflow as well - and try to cross ventilate via the open window.