Venting Help (Video inside)

[woodhouse]

I have a detached 25x16 garage that was built in about 1950ish

I plan on semi finishing it with no intentions of adding heating or cooling
I think I'm going to be plywooding the walls and leaving the ceiling open

That being said I want to make sure I have sufficient ventilation to battle the heat
I will be redoing the roof and thought maybe I should put a ridge vent in, but not sure how that will serve me in the winter if I'm leaving the ceiling open
I also have no soffit to add venting to

I think the best bet would be to add a gable vent at each end of the garage (there are tiny ones there now that are not functional) and add an exhaust fan at one end, something like this

Here is a video of the inside of the garage:

 

[fitter30]

Radiate barrier under the shingles would help.

Radiant Barrier Sheathing | LP® Structural Solutions

Radiant barriers are important components of a roof's construction. Discover the impressive energy efficiency of building with a premium radiant heat barrier.

lpcorp.com

 

[LWB]

You can do gable vents at either end or the ridge vent but to cut down on heat I'd insulate the ceiling. I will be doing this to a very similar looking building shortly. It made a huge difference in my shed. 8 x 12. You could feel the difference in temps just walking in and out of it.

 

[billconner]

If you're concern is heat in the summer and you don't want to insulate and cover interior surfaces, a gable exhaust fan on a thermostat would be simple and effective. I would prefer a ceiling and cellulose on it as more effective year round, easy to make comfortable with a small plug in electric heater in winter, but costs more and dose reduce volume.

 

[TonyG109]

It appears that the roof is exposed to direct sun so I'm guessing that radiant heat from the underside of the roof is going to be a major source of heat, especially because of it's close proximity. You said you're probably going to leave the ceiling open, but like billconner said, you may want to consider putting a ceiling in even if you don't insulate it (but insulation is always your friend). You'll definitely need to now vent the attic that was created by the ceiling since we have now trapped all the heat up there. Whatever you do, please keep us updated as to what you do and its effectiveness.

 

[woodhouse]

Radiate barrier under the shingles would help.

Radiant Barrier Sheathing | LP® Structural Solutions

Radiant barriers are important components of a roof's construction. Discover the impressive energy efficiency of building with a premium radiant heat barrier.

lpcorp.com

This is a cool option I didn't know about, but I don't plan on ripping the existing sheathing

You can do gable vents at either end or the ridge vent but to cut down on heat I'd insulate the ceiling. I will be doing this to a very similar looking building shortly. It made a huge difference in my shed. 8 x 12. You could feel the difference in temps just walking in and out of it.

I'm assuming the shed you had didn't have a ceiling either and you insulated directly on the underside of the roof? These rafters are 2x6 so most I could really get in there is r19

If you're concern is heat in the summer and you don't want to insulate and cover interior surfaces, a gable exhaust fan on a thermostat would be simple and effective. I would prefer a ceiling and cellulose on it as more effective year round, easy to make comfortable with a small plug in electric heater in winter, but costs more and dose reduce volume.

It appears that the roof is exposed to direct sun so I'm guessing that radiant heat from the underside of the roof is going to be a major source of heat, especially because of it's close proximity. You said you're probably going to leave the ceiling open, but like billconner said, you may want to consider putting a ceiling in even if you don't insulate it (but insulation is always your friend). You'll definitely need to now vent the attic that was created by the ceiling since we have now trapped all the heat up there. Whatever you do, please keep us updated as to what you do and its effectiveness.

I understand that putting a ceiling in would help drastically, but here's my issue

The original ceiling height in this garage was 7ft and felt extremely claustrophobic, so I got bigger lumber and raised the joists to get a little over 8ft and it feels 10x better in there

If you watch the video you'll see the last 3 joists I left at 7ft height to build a little loft at the end of the garage for car parts

If I did want to finish the ceiling, I'm not quite sure how I would finish that off and keep the storage

 

[TonyG109]

I understand that putting a ceiling in would help drastically, but here's my issue

The original ceiling height in this garage was 7ft and felt extremely claustrophobic, so I got bigger lumber and raised the joists to get a little over 8ft and it feels 10x better in there

If you watch the video you'll see the last 3 joists I left at 7ft height to build a little loft at the end of the garage for car parts

If I did want to finish the ceiling, I'm not quite sure how I would finish that off and keep the storage

Yeah, I did notice the last three joists but it didn't quite register in my head! Possibly putting in some sort of reflective barrier (reflective foam?) just on the bottom of your new horizontal collar ties would at least cut down on radiant heat from the roof and give you the headroom you need. Maybe even continue the barrier part way down the bottom side of the roof rafters and leave 6" or so at the bottom near the top of the walls for upward convective air flow. This, in conjunction with a good ridge vent, should help redirect the hot air up and out.

As far as the storage area...

Seal off the vertical triangular area created by the last new collar tie and two roof rafters. This will contain that hot air and force it to flow out the ridge vent.

In the storage area, put a reflective barrier on the bottom of the roof rafters, again leaving a few inches open at the bottom near the top of the walls to allow air to flow upward and out the ridge vent.

This whole scenario is venting to the ridge vent using inside air instead of outside air through the soffit. A little experimentation may be in order. Since you have no intention of heating in the winter, this may work.

 

[LWB]

Yes, I insulated directly on the ceiling.

A 2" air gap and a ridge vent would be optimal as long as you have a fresh air draw. I didn't have any issues though.

 

[woodhouse]

Yeah, I did notice the last three joists but it didn't quite register in my head! Possibly putting in some sort of reflective barrier (reflective foam?) just on the bottom of your new horizontal collar ties would at least cut down on radiant heat from the roof and give you the headroom you need. Maybe even continue the barrier part way down the bottom side of the roof rafters and leave 6" or so at the bottom near the top of the walls for upward convective air flow. This, in conjunction with a good ridge vent, should help redirect the hot air up and out.

As far as the storage area...

Seal off the vertical triangular area created by the last new collar tie and two roof rafters. This will contain that hot air and force it to flow out the ridge vent.

In the storage area, put a reflective barrier on the bottom of the roof rafters, again leaving a few inches open at the bottom near the top of the walls to allow air to flow upward and out the ridge vent.

This whole scenario is venting to the ridge vent using inside air instead of outside air through the soffit. A little experimentation may be in order. Since you have no intention of heating in the winter, this may work.

Yeah not having soffits to use in this case makes it more tricky
While the garage is far from air tight, I don't think it has the required fresh air openings to pull air up to the ridge which is why I was originally thinking a powered gable mount with a fresh air openings on the opposing side
But I do understand your thought process on this

Yes, I insulated directly on the ceiling.

A 2" air gap and a ridge vent would be optimal as long as you have a fresh air draw. I didn't have any issues though.

my problem is getting the proper fresh air draw for the ridge to work properly
even if I cut gable vents in, I don't think they would be low enough to properly draw all the heat up to the ridge

 

[LWB]

Ya, Ideally it would come from the Soffit.

I wouldn't hesitate going right against the roof. But, that's not the ideal way. IF, you have excess moisture in the room AND it travels through the insulation to a cold surface you could have a problem.

I'm not a big fan of vapour barriers myself. They trap moisture inside any structure unless you have a method to get rid of it. Moisture retarders are more suited to garages and older homes IMHO, which can be done as simple as using the right paint.

I'm renovating an old, really old, home right now and there won't be any plastic vapour barrier in it. I've already removed it from the block wall in the basement and found some mold behind it. Surprise...

 

[bowtie327]

I had a garage like just yours in my first home (1940’s built located in upstate NY). I added 2” round vents in the fascia (every other rafter bay) on both sides of the garage and a ridge vent. Then stapled an aluminum radiant barrier to the underside of the roof decking. No vapor barrier or insulation. Made a dramatic difference in the temperature inside the garage.

 

[woodhouse]

Ya, Ideally it would come from the Soffit.

I wouldn't hesitate going right against the roof. But, that's not the ideal way. IF, you have excess moisture in the room AND it travels through the insulation to a cold surface you could have a problem.

I'm not a big fan of vapour barriers myself. They trap moisture inside any structure unless you have a method to get rid of it. Moisture retarders are more suited to garages and older homes IMHO, which can be done as simple as using the right paint.

I'm renovating an old, really old, home right now and there won't be any plastic vapour barrier in it. I've already removed it from the block wall in the basement and found some mold behind it. Surprise...

I feel the same exact ways about vapor barriers....I just renovated a 1950s home and opted not to use them
I used rockwool instead and in the north east a class 3 vapor barrier is recommended and a latex based paint over taped sheetrock is considered one so that's what I went with

I had a garage like just yours in my first home (1940’s built located in upstate NY). I added 2” round vents in the fascia (every other rafter bay) on both sides of the garage and a ridge vent. Then stapled an aluminum radiant barrier to the underside of the roof decking. No vapor barrier or insulation. Made a dramatic difference in the temperature inside the garage.

I never though drilling those vents through the fascia! Only issue is that it would essentially be blocked by the gutters

 

[BillK]

maybe I should put a ridge vent in, but not sure how that will serve me in the winter if I'm leaving the ceiling open
I also have no soffit to add venting to

My detached garage is all open inside and has a ridge vent. Does not seem to cause any type of problem and gets some of the hot air out in the summer. You are a lot further north than I am and really should be fine with just that.

Guys are mentioning vapor barriers, insulation etc ????? I might be wrong but if you are not planning on heating or air conditioning I dont see what the reason for any of that would be.

 

[LWB]

Roof insulation will keep down the summer heat.

 

[woodhouse]

My detached garage is all open inside and has a ridge vent. Does not seem to cause any type of problem and gets some of the hot air out in the summer. You are a lot further north than I am and really should be fine with just that.

Guys are mentioning vapor barriers, insulation etc ????? I might be wrong but if you are not planning on heating or air conditioning I dont see what the reason for any of that would be.

I think the thought it to make a separation between the roof and work space and that any type of barrier will help keep the heat up and out rather than in the working area

your ridge has fresh air inlets in the soffit I'm assuming?

 

[billconner]

I believe you're not insulating and not heating or air conditioning, And you'd like to not let it get ****** hot in the summer and don't really want the looks let alone cost of a ceiling. A simple gable exhaust fan will pull off that high heat. The underside of the roof sheathing will sill radiate heat, but I think any measures to lessen that will simply lead to other problems. Lighter roofing color would help.