Heat in second floor of 1.5 story?

CabinNick · December 11, 2015, 10:17:13 PM

Curious to hear other's opinions on an issue. I have been planning on building a cabin with an expanded version of the 20x30 1.5 story plans. We were thinking about having the full second floor instead of a loft. To save on cost and make a simpler build, we were not planning on having any dormers so there would just be windows on two ends of the second floor. We will be off the grid on a smallish solar system so there will be no AC and probably not any ceiling fans.

We are a little worried that the second floor will get unbearably hot in the summer. We live in eastern Oregon at about 3800'. There is no humidity but our summers are usually full sun and summer days are typically in the 90's but it cools off into the high 40's at night a lot of times.

What have others experienced with heat build up from sun during the day in your 1.5 story? Is it a big enough issue that we should consider having only a 1 story.

I hate to say it but we have ice in our blood - we hate the heat and would probably be better suited living in Alaska!

firefox · December 12, 2015, 06:35:35 PM

Just an idea. Possible put a bunch of those spiiner vents along the ridge. Not
sure about the name, but the look like a ball that has had its sides slit and bent
to make vanes. The rising heat makes them spin and help remove the hot air.

December 12, 2015, 06:56:11 PM

Quote from: firefox on December 12, 2015, 06:35:35 PM
Just an idea. Possible put a bunch of those spiiner vents along the ridge. Not
sure about the name, but the look like a ball that has had its sides slit and bent
to make vanes. The rising heat makes them spin and help remove the hot air.

These things?

firefox · December 13, 2015, 12:10:11 PM

Yep. Thanks azgreg!

NathanS · December 13, 2015, 01:32:58 PM

My 2 cents

Those things are supposed to help airflow of unconditioned air in a ventilated attic/roof.

They can depressurize the attic (or ventilation channels in a cathedral ceiling) and suck warm air out of the house... This is a bad thing in the winter and can cause ice damming.. which, funny enough, is what those things are trying to prevent.

If it was me, I would do more than just insulate the rafter bay. I would use a good bit of rigid insulation, and then I'd fur out the top of the roof for proper ventilation. Good air sealing details would also go a long way.

Ceiling fans are by far the most energy efficient way of making an area more comfortable. You could definitely run one or two off a small battery bank. Especially considering the days when you need to cool off are the most 'solar productive' days as well.

December 13, 2015, 04:52:54 PM

In my opinion the mini-split heat pump has mostly changed how I look at conditioning space. Build a good house that will last and add a split heat pump. They are over 30 SEER now and easy to install. No ducting and I have a few clients with a similar 2 floor plan. They just cool the top floor and the cold air spills down to the first floor. Sometimes a small air circulating fan/duct can be used if there are long hallways. Run it off a KW or 2KW of solar and you do not have to worry about much for cooling. They heat really well also but you really need a second source of heat downstairs for winter, in my opinion.

firefox · December 13, 2015, 09:50:01 PM

I was wondering if they made a door or cover for those things for the winter.

flyingvan · December 13, 2015, 10:23:32 PM

I'm getting to be a bigger and bigger fan of radiant barrier material. Here, you're required to have it from the highest living space up (essentially the rafters and gable ends). Our attic is cool all Summer. I even used it in the porch roof. I'm trying out the mylar faced OSB on a small shed project right now, but I prefer the rolled two ply stuff with the bubble wrap inside. It's only effective with an airspace, so the rolled stuff you can lay loosely over the rafters prior to roof sheathing. You need to be aware of airflows above and below since it doesn't breathe at all and even in dry climates you can trap moisture
Do people use swamp coolers in that area?

CabinNick · December 17, 2015, 12:06:41 AM

Thank you all for the suggestions. I am going to research the radiant barrier. Sounds like a good option for us to consider.

January 14, 2016, 01:11:26 PM

I was reading this article and it made me think of this thread.

http://www.greenbuildingadvisor.com/blogs/dept/musings/fans-attic-do-they-help-or-do-they-hurt

Oregon would actually be a perfect place for a 'whole house fan'. Once it is nice and cool in the evening, you fire it up for an hour or so and it will get your house down to temperature.

It also explains why attic fans are are a bad thing in a lot of detail.

CabinNick · January 15, 2016, 12:46:51 AM

Good article, thanks for the link. That would probably work great for us. It is amazing how our summer temps fluctuate throughout the day, not uncommon to have daytime highs in the 90's and then down in the 40's at night. The problem is getting any kind of draft in the windows to cool down the house once the outside temps finally drop.

OlJarhead · January 15, 2016, 12:48:36 PM

We're in Eastern WA and at about 3000 feet. Our loft can get warm in the summer during the hottest part of the day but it's not usually too bad. What we do in the summer is open the loft windows during the cool periods as well as lower level windows, then when it starts to warm up we close all the windows and use heavy curtains with blackout sheets on the sun side. Keeps the cabin nice and cool throughout the day and only on the hottest days does it finally start to get warm inside. Usually it approaches equalization around 4pm (meaning inside and outside temps are the same) when the outside air temp is starting to drop. Within a couple hours we open windows again and get the air moving.

We also have a 12/24v DC ceiling fan that we can run off the solar to help draw warm air up or push cool air down.

firefox · January 15, 2016, 05:16:15 PM

With respect to the whole house fan cover. For low budget DIYs here is an idea
Make a insulated cover.
Put some screw eyes in the corners.
Attach 4 vertical rods to the sides of the fan enclosure lined up to fit the screw eyes
in the cover to act as guides.
Make a wire lifting harnes by attaching four wires to the cover by wraping around the
shank of each screw eye and then securing the other end to a ring over the center of the
cover.
Attach a wire cable to the ring and thread it to an over head pulley secured to a rafter
and bring the cable down thru a small reinforced hole in the ceiling to a clete on the wall.
(you can get stainless wire rope with covering from your local store as well as small pulleys etc.)
If it is really heavy you might want to improvise a crank.
Hope this helps someone.

Dave Sparks · January 21, 2016, 03:32:56 PM

Quote from: CabinNick on January 15, 2016, 12:46:51 AM
Good article, thanks for the link. That would probably work great for us. It is amazing how our summer temps fluctuate throughout the day, not uncommon to have daytime highs in the 90's and then down in the 40's at night. The problem is getting any kind of draft in the windows to cool down the house once the outside temps finally drop.

That is the problem that the mini split solves. The house never gains any heat ! You just set it to 75F or so and shut it off at sundown and open windows. If you have grid power it really is a no brainer. Offgrid it takes a bit of planning. They are so cheap to run and they keep the dust out among other attributes.