insulation

[SGKent]

background:
am going to deep bury the HVAC ducting, add rafter vents, and more insulation to the attic. Single story built in 1979. Tyvek and new siding added in 2003. New ducting in 2004 but it gives a blast of heat when it has been sitting. If I leave the fan on with the AC off the temps in the house rise by 5 or 6 degrees more than with the AC off so I know that the R6 ducting is carrying heat into the house. Plenty of attic venting, you can walk up there on a hot day.

Here is the question:
The original insulation from 1979 is 4" of cellulose blown in that has settled. In 1991 when I bought the home I laid r-19 over it. It has compacted as well over time with people working in the attic, time etc. Does one think it would be better to pull it all out, put in the rafter vents, seal up the cable, Cat 6, electrical holes etc. and put in new insulation, or just put insulation over what is there now? I also want to build some sort of a 18" or so cat walk the length of the attic across the rafters so if someone has to go up there they can walk without trying to follow the rafters without putting their foot thru the floor. I am too big and old these days to be climbing around up there so I'll have to hire an insulation company.

We are in a suburb of Sacramento in NorCal. It will be 93 F today. It was 108 F Sunday. Winters are mild, typically lows of 25 F to 35 F, occasionally a year to 18 F. Highs can hit an occasional 110 F - 112 F in summer. Dual pane glass and R 13 in the walls. Insulated and drywalled garage.

 

[yeldogt]

Why don't you insulate the roof and be done with it ..? no vent. That's what I have been doing for 25+ years with all my projects.

 

[SGKent]

Why don't you insulate the roof and be done with it ..? no vent. That's what I have been doing for 25+ years with all my projects.

because it cooks the roofing tiles and wood under them in this climate. Strictly a no-no.

 

[strutaeng]

because it cooks the roofing tiles and wood under them in this climate. Strictly a no-no.

What type of roof tile? If clay tile, should not be a problem. Also, wood deck is not a problem with attic heat, regardless of where the insulation is installed.

I was going to suggest just adding more insulation in the attic. Don't mess around with adding additional venting.

 

[yeldogt]

because it cooks the roofing tiles and wood under them in this climate. Strictly a no-no.

They do it all over the world ...

Cook wood ... tile? What about trees and tile goes in a kiln.

My house in SA is tiles (concrete) .. no vent.

 

[SGKent]

fiberglass shingles with tar paper underlay.

 

[strutaeng]

At my old house I added masonite-made baffles and a bunch of soffit vents. I only had gable vents. House is 2,000 sq ft with attached 2 car garage, one story. I was like you and only had about 4-6" of insulation. I added blow-in cellulose to a total of like 10".

I honestly didn't see any difference before or after the soffit vents. It was still hot as hell in the attic. That's just the nature of attics. I have said this before, attic venting is not meant to "cool" the attic. It was a response to control condensation from conditioned air leakage. Unless you go into your attic and see mold and mildew, don't mess with it. Also, I'm not a fan of attic vent due to insect, dust and noise issues. Non-vented attics are always going to stay cleaner than vented equivalent.

If you read the literature, the attic ventilation equations are not from analytical models or research, just some prescriptive requirements.

Just do your air sealing and add more insulation. You don't have to remove all of the insulation for air sealing. Pay extra attention to soffits and recessed lights.

 

[SGKent]

you've given me an idea how to add rafter vents from a piece of masonite and L brackets then I need to move one cable in the attic and have someone come in and add insulation.

For the whole house fan I had to add vent space so I added an additional gable end vent to each gable, two low profile roof vents and more soffit vents. The temp in the attic dropped probably from about 150 F to about 105 F on hot days. Now I just need to get the HVAC ducting under the insulation too so I am not losing cooling to the attic space. Thanks for the suggestion.

 

[yeldogt]

Does CA do energy audits w/ recommendations?

Blower door tests?

It's interesting when blower door tests are done in houses with vented crawl spaces and attics. OH my. And, when they do testing with attic fans running ....

That's the way we always do it .. hard to change.

 

[Jackfre]

Careful of the attic vents. I'm in Nevada City and kinda in the crosshairs from a fire perspective. You are too, I assume. Check out this video:

I ripped the roof off my last wooden building yesterday to fire harden. I will raise the pitch and go metal and then hard board and batten. At that point everything will be metal, Hardie, or class A roofing. Defensible space is good. My weakness as i see it is the gable vents and soffit vents. The video shows the ember storms and the problem is that they operate in a fluid dynamic manner. I am currently covering all of them with 1/8" screening. Fingers crossed.
As to your insulation, I would clear the attic of all the old matted **** and start fresh. It will be a hell of a mess. You the know what you have and the difference will be remarkable. I did this in my MA home and was very pleased with the results. It also allows you to see what is really up there and add/correct. It is a good time to install a whole hose fan. The raised cat walk is also a good idea...if you have the head space.

 

[strutaeng]

Careful of the attic vents. I'm in Nevada City and kinda in the crosshairs from a fire perspective. You are too, I assume. Check out this video:

I ripped the roof off my last wooden building yesterday to fire harden. I will raise the pitch and go metal and then hard board and batten. At that point everything will be metal, Hardie, or class A roofing. Defensible space is good. My weakness as i see it is the gable vents and soffit vents. The video shows the ember storms and the problem is that they operate in a fluid dynamic manner. I am currently covering all of them with 1/8" screening. Fingers crossed.
As to your insulation, I would clear the attic of all the old matted **** and start fresh. It will be a hell of a mess. You the know what you have and the difference will be remarkable. I did this in my MA home and was very pleased with the results. It also allows you to see what is really up there and add/correct. It is a good time to install a whole hose fan. The raised cat walk is also a good idea...if you have the head space.

Yikes! That's crazy! At minute 3:39...


The video states even with 1/8" screen, the embers came in. Don't you want to use a finer screen? Maybe a S.S. mesh or sieve. That will quickly get expensive though.

 

[yeldogt]

That's a good video ... take the fire away and this shows why vents don't work. Everybody thinks the heat goes up and out .. pulled through the soffits .... venting looks good on paper. But, what happens when there is ANY wind. The attic pressurizes and pushes attic air into the house.

Same thing happens in the crawl.

I do metal roofs and Hardie as well -- people don't understand how flammable vinyl can be .. the gutters act like a fuse.

 

[strutaeng]

That's a good video ... take the fire away and this shows why vents don't work. Everybody thinks the heat goes up and out .. pulled through the soffits .... venting look good on paper. But, what happens when there is ANY wind. The attic pressurizes and pushes attic air into the house.

Same thing happens in the crawl.

I do metal roofs and Hardie as well -- people don't understand how flammable vinyl can be .. the gutters act like a fuse.

True. I think OP mentioned he has an attic fan? And attic is 105F? That doesn't sound right. It may be that the fan is sucking conditioned air into the attic, thereby resulting in a net loss from an energy standpoint.

Attics (unconditioned) around here are in the 120-130F range, vented or not.

I've been into some conditioned attics insulated with spray foam, and even those are lows to mid 90Fs.

 

[SGKent]

True. I think OP mentioned he has an attic fan? And attic is 105F? That doesn't sound right. It may be that the fan is sucking conditioned air into the attic, thereby resulting in a net loss from an energy standpoint.

Attics (unconditioned) around here are in the 120-130F range, vented or not.

I've been into some conditioned attics insulated with spray foam, and even those are lows to mid 90Fs.

There is enough air circulating thru from the soffits to the gables and low profile eyebrows that the temps stay down as long as you don't stick your head up near the top of the roof. I also replaced the roof shingles with a lighter color when the house was reroofed in 1996. It is due again. The whole house fan has louvers inside that close when it is off. They have foam seals on each vane. The problem is in part that the cost of electricity has gone sky high in California this year because certain people want to offset the use of it with high carbon taxes on the middle class that can be used to fund healthcare for all. The cost in the early morning is 1/3 what it is between 5-8pm when the middle class is coming home from work to houses where the AC has been off all day. Kids have school work and there are meals to cook for most. I am retired so can do the family chores that take power before noon but I hate giving the money to a political party so they can use it to do nothing more than give it to people who can't even legally be here just so they can get more votes. This state is becoming the Mexican - American war in reverse where California is going back to Mexico which signed it over to America in 1848. I'd like to avoid losing money to this strategy. I'd rather pay a local company to replace the insulation than pay for more power lost to lack of the best insulation.

I am leaning towards having all the old insulation taken out and new put in.

As to fire risk - I wish I could say we aren't in a fire zone where I live but all of California is a fire zone and Santa Rosa proves that it doesn't matter how urban you are - with the amount of fuel that has built up because the radical environmentalists would like to see everything au natural, every home in California is at risk. I have removed all the big trees from near the property, live in a subdivision in Sacramento County where it is almost all subdivisions but fire embers can carry from a very long way.