Energy Efficiency Ideas -- Attic

[nwdiver]

My house currently has no insulation at all (very old house). While we live on coastal area the temperature fluctuates a lot during the hottest / coldest days. I have been thinking about insulation but not sure which to go with. As mentioned the house does not have insulation whatsoever so will the attic insulation help much? The walls are still not insulated.

I also like to run/add my own network cables every once in a while, will the blown insulation be applied at the attic floor? If yes that will interfere if I decided to run more cables. If it's only applied below the roof then doesn't that also seal in the heat trapped inside the attic?

Spray foam is certainly superior in terms of R-Value per inch. But if you have the room in your attic for a foot or so of cellulose it's ~1/4 the cost. Cellulose will also settle limit air flow through the ceiling. Most homes don't have insulated walls.

You can find blown cellulose at Lowes or Home Depot. If you buy ~20 bags you can typically get the blower for free. With the help of a friend to feed the blower you can usually insulate ~1000sq ft in <2 hours.

My local hardware store included a blower rental with purchase of a pallet of cellulose insulation. Did the DIY blown cellulose job with my wife almost 10 years ago. I made a "slight" miscalculation, meant to add 2' of insulation, but ended up with 4' .. oops, a little more doesn't hurt. Dropped out heating/cooling bills dramatically. Total cost $300.

Yep... adding the recommended thickness of cellulose to your attic is the #1,2 & 3 best things you can do IMO. So cheap. So effective.

 

[Xenoilphobe]

I did cellulose at my old house - unfortunately in my case it didn't help - my issue was an 24 x 20 bedroom above a garage and the air flow was leaking all the heat out the bottom of the room - we ended up moving to a new home, but if I had known about spray foam I would have done the garage instead and it would have resolved the air leakage issues...

Cellulose is a good option too... each case is different.

 

[nwdiver]

Is that a given ? I understand that air will not flow up, but it could still flow sideways through vents if the goal is ambient. My implied bias is to avoid heat transfer from the hot asphalt shingles.

I take it that the radiant barrier does not cover the apex of the attic where the ridge is placed ? What fraction of the attic heat is from radiation alone ?

Sorry for the dumb questions. I am not well informed but would like to be!

Not sure how to do the calc but I would imagine the heat in the attic is probably ~80% radiant. The roof easily gets >150F. You're not gonna get an attic cooler than outside air temps... it wouldn't be worth it. Yes, there should be a gap at the top and bottom of the radiant barrier to allow for air flow.

Cellulose is a good option too... each case is different.

True... I have a flat roof above my living room... no way to blow cellulose into it

 

[SDRick]

I recently installed a couple of Airscape ducted attic fans. I chose them over the Quiet Cool system although they were close in specifications. The Airscape brand offers 10 speeds (vs 4) and had some other nice features. I typically run at the lowest speed all night consuming only 35 W per fan. These newer style attic fans do a great job of quietly bringing in cool outside nighttime air for a fraction of the cost of running the AC.

As an additional benefit, the fan creates positive pressure in the attic forcing out accumulated hot air through all the attic vents.

 

[nwdiver]

As an additional benefit, the fan creates positive pressure in the attic forcing out accumulated hot air through all the attic vents.

Hmmm... not sure positive pressure in the attic is a good thing... might want to check your house with an IR camera. Hot air can bleed into all sorts of places when the pressure in the attic is slightly higher then the pressure in your house.

Like down walls and out electrical outlets....

OR out of ceiling mounted smoke detectors...

This is another reason I'm not a fan of active ventilation (no pun intended)

 

[Xenoilphobe]

Not sure how to do the calc but I would imagine the heat in the attic is probably ~80% radiant. The roof easily gets >150F. You're not gonna get an attic cooler than outside air temps... it wouldn't be worth it. Yes, there should be a gap at the top and bottom of the radiant barrier to allow for air flow.



True... I have a flat roof above my living room... no way to blow cellulose into it

If you live in a hot climate you can always paint it white and add the insulation on the exterior, using PVC Membrane – aside from the membrane itself, an insulation board must first be installed to help with energy costs. The membrane is installed in rows (6-18′), each of which must be hot-air welded at the seams. Many contractors choose to mechanically fasten the edges to help prevent uplift, all of which contribute to labor costs. All in total, installation of a PVC membrane costs roughly $7.00 to $10.00 per square foot. Flat Roof Materials & Costs: PVC vs. TPO, EPDM, Plus Pros & Cons

 

[nwdiver]

If you live in a hot climate you can always paint it white and add the insulation on the exterior,

I did the first best thing

 

[abasile]

I did the first best thing

Indeed, our rooftop solar, by effectively shading our roof, has made our home significantly more comfortable during the summer. (Not all of our home is insulated as well as the attic that I describe upthread.)

 

[Xenoilphobe]

I did the first best thing

View attachment 245626

I call that living in the shade! In New Mexico this should be mandated as code as well for all new construction.

 

[nwdiver]

I call that living in the shade!

Yeah...but it doesn't help in the Winter... or when the AIR temp is 105F

 

[Skotty]

What about attic fans? Our house has an attic fan. It's nice for about 2 weeks in the spring and fall when temperatures are actually in the desirable range, but the rest of the time it's a giant hole with no insulation other than the vent slats that close. Should I maybe cover it when not in use?

By the way, here's the first round of temp readings from the attic (I'll continue taking readings until dark, plus do it on other days with other outside temps) -- this is for a mostly sunny day:

Time / Inside Temp / Outside Temp / Attic Temp
10:30a / 74.8 / 86.4 / 88.2
11:00a / 74.7 / 86.7 / 92.7
11:30a / 74.5 / 88.0 / 97.5
12:00p / 74.5 / 87.8 / 103.6
12:30p / 74.5 / 89.4 / 109.4
1:00p / 74.3 / 90.3 / 112.6
1:30p / 74.1 / 91.2 / 117
2:00p / 74.1 / 91.4 / 119.5
2:30p / 74.1 / 91.2 / 121.5
3:00p / 74.3 / 91.2 / 123.1

We have gas heat but electric A/C. The difference between a winter month electric usage and mid summer month, at least from the 2016-2017 timeframe, is about 1500 kWh per month (July and August). I'm guessing that's bad. For example, March 2017 electricity usage was 1579 kWh, while August 2016 was 3126 kWh.

 

[nwdiver]

What about attic fans? Our house has an attic fan. It's nice for about 2 weeks in the spring and fall when temperatures are actually in the desirable range, but the rest of the time it's a giant hole with no insulation other than the vent slats that close. Should I maybe cover it when not in use?

I don't think there's much benefit to the home in regulating the temperature of your attic. It's counter intuitive but heat transfer isn't linear. The actual heat transfer is the reciprocal of the R-Rating. As long as your ceiling is well insulated the temperature of your attic has a negligible effect on the heat transferred into or out of your house. Air leakage has a significantly larger effect.

If the choice is $200 for an attic fan or $200 for an additional R-6 of cellulose the cellulose is a much wiser investment...

 

[Skotty]

I don't think there's much benefit to the home in regulating the temperature of your attic. It's counter intuitive but heat transfer isn't linear. The actual heat transfer is the reciprocal of the R-Rating. As long as your ceiling is well insulated the temperature of your attic has a negligible effect on the heat transferred into or out of your house. Air leakage has a significantly larger effect.

If the choice is $200 for an attic fan or $200 for an additional R-6 of cellulose the cellulose is a much wiser investment...

Let me clarify. There are 2 different kinds of fans I have been taking about here. The one between the attic and the outside, which is the one I was talking about earlier on that I was considering for helping lower attic temp, and the one between the interior and the attic, which is the one I was talking about in my previous post. For the latter, there basically is no insulation. It's a hole with a fan it, and only the metal slats to seal it off from the attic. My house already has one of those, and I'm curious if it might be a problem area.

EDIT: Minor correction, those "metal" slats just look metal. They are actually plastic. I just touched them to see if they feel hot. Felt a bit warm, but not hot.

 

[nwdiver]

Let me clarify. There are 2 different kinds of fans I have been taking about here. The one between the attic and the outside, which is the one I was talking about earlier on that I was considering for helping lower attic temp, and the one between the interior and the attic, which is the one I was talking about in my previous post. For the latter, there basically is no insulation. It's a hole with a fan it, and only the metal slats to seal it off from the attic. My house already has one of those, and I'm curious if it might be a problem area.

What's the purpose of the fan from the interior to the attic? Ventilation for the house? That's odd... don't think I've ever seen that before... Some central air systems have 'economizers' that draw in outside air to keep air in the house fresh... I wonder if that's the purpose...

 

[Skotty]

What's the purpose of the fan from the interior to the attic? Ventilation for the house? That's odd... don't think I've ever seen that before... Some central air systems have 'economizers' that draw in outside air to keep air in the house fresh... I wonder if that's the purpose...

Far as I know, it's just something for those days where it's cool enough to not run your A/C but warm enough it's still uncomfortable not to. On such days, people like to leave the A/C off, open some windows and turn on the "attic fan". It draws in air through the windows and pushes it out into the attic.

Here's a couple of pictures.

There's a giant fan above the white slats. When you turn it on, the slats are drawn upward by the fan, but they are hinged on one side of each slat, so the air pressure created by the fan opens it like a vent, and then they drop back down from gravity when fan is turned back off. You can turn it on high or low, and set a timer for it.

Size of the hole is about 3 feet by 2.5 feet, with no insulation or barrier other than the plastic slats.

 

[Xenoilphobe]

I need one of those in the den for smoking cigars!!!

 

[nwdiver]

Far as I know, it's just something for those days where it's cool enough to not run your A/C but warm enough it's still uncomfortable not to.

Ah... that's pretty neat. That would be handy in the evenings when you get home and it's 70F outside but 80F inside.

Adding a fan to the attic miiiiight help the fan blowing into the attic a little since they would be kinda working in series... but the temperature in the attic wouldn't be the issue. It would be a question of how hard the fan blowing air into the attic is working. Even then... I think adding more paths from the attic to the outside passively with a ridge vent would be more effective. I would be interesting to measure the positive pressure in the attic with the fan working. Do you have a barometer?

A few years ago I ran the numbers on how much money I was saving just from the shade from the panels on my house. It was something like ~$0.50/mo... that led me to realize that radiant barriers don't save much (if the ceiling is well insulated). Which led me to realize that the temperature of the attic is mostly irrelevant (if the ceiling is well insulated).

Hot air from the attic can only heat your home thru conduction. With a sufficient R-Rating the difference in temperature has a negligible effect on heat transfer.

 

[Skotty]

Ah... that's pretty neat. That would be handy in the evenings when you get home and it's 70F outside but 80F inside.

Adding a fan to the attic miiiiight help the fan blowing into the attic a little since they would be kinda working in series... but the temperature in the attic wouldn't be the issue. It would be a question of how hard the fan blowing air into the attic is working. Even then... I think adding more paths from the attic to the outside passively with a ridge vent would be more effective. I would be interesting to measure the positive pressure in the attic with the fan working. Do you have a barometer?

A few years ago I ran the numbers on how much money I was saving just from the shade from the panels on my house. It was something like ~$0.50/mo... that led me to realize that radiant barriers don't save much (if the ceiling is well insulated). Which led me to realize that the temperature of the attic is mostly irrelevant (if the ceiling is well insulated).

Hot air from the attic can only heat your home thru conduction. With a sufficient R-Rating the difference in temperature has a negligible effect on heat transfer.

You haven't really commented on the giant hole issue of the attic fan. I think maybe I could build an insulated box around the fan, maybe even with a gravity flap that lifts up when the fan is on and falls back down when it's off. Using some kind of stiff insulation board.

 

[SDRick]

There's a giant fan above the white slats. When you turn it on, the slats are drawn upward by the fan, but they are hinged on one side of each slat, so the air pressure created by the fan opens it like a vent, and then they drop back down from gravity when fan is turned back off. You can turn it on high or low, and set a timer for it.

Size of the hole is about 3 feet by 2.5 feet, with no insulation or barrier other than the plastic slats.

Not sure if it will pay for itself in your situation, but I have seen insulated and powered dampers available for both new and older style whole house fans.

 

[nwdiver]

You haven't really commented on the giant hole issue of the attic fan. I think maybe I could build an insulated box around the fan, maybe even with a gravity flap that lifts up when the fan is on and falls back down when it's off. Using some kind of stiff insulation board.

Kinda did....

I don't think there's much benefit to the home in regulating the temperature of your attic.

If you're installing a fan from the attic to the outside I wouldn't worry about the hole. I DO think there is probably a benefit to insulating and/or sealing the exhaust fan into your attic (in the winter). There's a good chance you're losing some heat thru those slats in the winter.