Insulating our attic?

[rharman]

We have an unfinished attic with a shed roof over part of our house. That attic is where the furnace & air conditioner reside. It's really hot in there. The floor of that attic is the ceiling of our living room and that is insulated (fiberglass batts). The roof faces West.

We're considering putting insulation in the roof rafters - likely Roxul. So....

1. Is that a good idea?
2. Does insulating the roof just trap the heat in the roof sheething and shingles - shortening the life of the shingles?
3. Do we need vents for airflow between the insulation and roof sheathing? There is no ridge vent - just gable vents on the ends. Vents: https://www.homedepot.com/p/ADO-Products-Provent-14-in-x-4-ft-Rafter-Vent-UPV14480/100533902

Keep in mind that this is Southern California. Most everything I read is geared towards cold climates and keeping heat in. I want the heat out.

Thanks.

 

[Kaizen]

Yes you can bring the whole space into the conditioned space. Remove floor insulation and insulate roof space. I saw a company use four inch hard foam panels screwed to the underside of the rafters. It’s on YouTube someplace. You can cut a ridge vent in to an exhausting roof. I would make sure it’s vented.
Or I believe spray foam negates the need for venting. Others can confirm.
Putting the equipment inside will make the house more comfortable as you are not losing efficiency in the attic ducts


Sent from my iPhone using Tapatalk

 

[yeldogt]

Does CA have energy audits ? Great way to get free or almost free information / inspection.

I always do conditioned attic and crawl spaces --- the attic is completely sealed. I use foam .. but other insulation can be use. I have done conventional previous to using foam.

When I have retrofitted -- the exiting insulation in the ceiling remained.

At one time shingle manufacturers did exclude unvented assemblies -- studies have shown the actual difference to be around 20 degrees. This between unvented and a properly functioning vented assembly ..... that almost never occurs. In most parts of the country that extra temp would still be under a vented in a hot climate .... in extremely hot climates asphalt is an issue ... even radiant barriers causes heat buildup.

Placing HVAC in unconditioned spaces is really dumb -- but, very common.

 

[DC73]

We're considering putting insulation in the roof rafters - likely Roxul.

Do yourself a favor and visit the GreenBuildingAdvisor website. Search for articles on unvented attics. Then, search their Q&A forum. You will find plenty of information. You can also pose your question on their forum and some of the building science gurus who hang out there will advise you.

You can do what you want but you have to get the details right to avoid condensation on the underside of your roof deck. Vapor permeable insulation such as fiberglass and mineral wool can allow water vapor to reach and condense on on the underside of the roof deck. Different climate zones have different needs. GBA will likely recommend a certain amount of foam either on top of the roof or just under the roof deck to avoid the condensation issue. The amount of foam needed is dependent on your climate zone.

You could also build a ventilation channel just under the roof deck along with full soffit and ridge vents if your roof construction allows. Then insulate under the vent channel with whatever insulation you want.

Here is a link to an article that might be of some value to you: https://www.finehomebuilding.com/2015/11/11/insulating-unvented-roof-assemblies

DC

 

[billie]

You need better/more attic ventilation.

Where is the AC condensor located? Are you adding heat?
But no, insulation is not your best choice.
Eliminate any heat sources.
And ventilate.

 

[strutaeng]

We have an unfinished attic with a shed roof over part of our house. That attic is where the furnace & air conditioner reside. It's really hot in there. The floor of that attic is the ceiling of our living room and that is insulated (fiberglass batts). The roof faces West.

We're considering putting insulation in the roof rafters - likely Roxul. So....

1. Is that a good idea?
2. Does insulating the roof just trap the heat in the roof sheething and shingles - shortening the life of the shingles?
3. Do we need vents for airflow between the insulation and roof sheathing? There is no ridge vent - just gable vents on the ends. Vents: https://www.homedepot.com/p/ADO-Products-Provent-14-in-x-4-ft-Rafter-Vent-UPV14480/100533902

Keep in mind that this is Southern California. Most everything I read is geared towards cold climates and keeping heat in. I want the heat out.

Thanks.

Can you just add more insulation on top of the existing fiberglass? Is it ceiling joists and rafters? Or trusses? You can lay down fiberglass perpendicular to existing. It's easier if area is open, as in ceiling joists. Trusses are more difficult because of all the diagonal webs.

So I think you need R38 insulation in your climate, roughly 12" combined.

I wouldn't worry about venting. The gable vents that you have are probably okay. Besides, your climate is more on the dry side. Attic venting is more for controlling condensation resulting from air leakage. If you read the articles on vented vs non-vented, they cite something like a 3F difference in temperature, which is marginal.

If you go up there and everything is moist and humid-smelling, then I would advice to install more vents, but I doubt it.