Home insulation question.

I have a bonus room that has insulation in the walls but while I was in the attic over the weekend has none in the ceiling. It appears someone did the blow-in stuff a long time ago but there is barely any of it there. Most of the ceiling drywall is exposed. I would like to do the roll-in stuff.

I suspect I don’t need it faced since it won’t be touching external walls. Does anyone know what thickness I would need? Is bigger always better in this instance? Like 6 inches is better than 4? The room gets a ton of direct sun so it heats up a lot in summer which is what I’m trying to solve for.

 

r38 or better. May want to check any inspection records. Seen where builders put the insulation cert on scuttle but dont actually put any in

 

Thicker will have a higher R value meaning you get less heat transfer and more insulation, blown in works well in sealing up all the voids but it does settle over time. You can buy bags a cellulose at HD and rent a machine to add more to what you have at a reasonable price

 

Don't overlook your attic venting.

 

Thanks

 

Look into a current product called Spider from Johns Manville. Has the benefit of blown in but bonds together and doesn't settle.

https://www.buildinggreen.com/blog/getting-know-spider-insulation

 

Yes

the area I will be doing has a vent but unfortunately the other areas have fans that kick one when they’re hot. I might try to install a fan in this area so long as it doesn’t negate the airflow from the others. Maybe I’d have to put one that sucks in air while the others pull the air out to get some actual air flow.

I need to give another look this weekend. Figured since it’s june gloom and rather cool still this time of year I want to get it done before the attic is hot.

 

I like wearing a banana hammock made of R-13.

 

I’ve used the bagged or encapsulated fiberglass insulation in the past. Keeps you from getting exposed to the fibers etc and helps reduce dust etc so your not breathing the stuff in as you carry it up through your small attack entry and install. Slightly more $ but worth it. I think it comes in 15 or 20 foot sections and vacuum packed so it doesn’t take up a lot of room until you unpack.

 

forgot to add.. make sure you have eave baffles 2' or better.
There is also an r30 foil looking stuff wide enough to run between rafters or trusses. Keeps the radiant heat at the deck/vent level.

 

Why don't you spray the under side of the roof with closed cell foam, put r-19 in the ceiling cavities, sheet the ceiling joists, and use that area for a somewhat temperature controlled storage area? You could kill 2 birds at the same time.

 

That’d be optimal but where it’s located and the access won’t allow it. I have storage over the whole other side of the house and garage so it’s not quite necessary.

I really just want the heat knocked down.

 

That just sounds very itchy.

 

You're on the right track here JZ. If there are currently eve vents, be sure to hold back your insulation a little so as not to block the flow of air. There should be venting for air in and venting for air out. The solar powered attic fans are not a bad way to go. You're like a mile from the beach, how hot can it be up there?

 

Thanks man. Yes - the sun bakes this room. I have to turn the AC on a few times a year.

 

Actually, you should add on chutes over the eave vents, to maintain airflow up the inside of the roof.

Then insulate, right up to the chute

This is critical in damp climates. Unless you like a moldy attic

 

Cellulose blow in with proper soffit and roof venting.

 

Just by a new house.

 

Cellulose has to be the nastiest shit ever to be used in home construction. Well, maybe next to asbestos.

Like everyone else is saying, venting is the most important part of the equation. Heat gain/loss sucks, but sucks less than a roof rotting from the inside out.

Closed cell is the bee’s knees, last I priced it out was $1.10/board foot, so multiply your roof square footage by that x the depth of spray you want and you’ll have a guesstimate for budgeting. Other beautiful thing about a hot roof is that you don’t have any fluffy, powdery, itchy or otherwise unpleasant shit to deal with should you need to get into your attic space for anything.

If hot roofing is out of your budget, and you’re hell bent on DIY’ing it, take the time to foam closed any ceiling penetrations (light fixtures, holes in top plates for wiring, plumbing, etc) and go nuts with blown in (I prefer the snowflake stuff to the shredded pink panther shit, since I get stuck crawling around in attics more than I’d like its nice to not feel like you’re covered in mosquito welts when you crawl back out). In a couple of years blow a few more bags in to account for settling.

Or go really nuts and cut sections of PIC (polyisocyanurate, AKA Thermax) to go between the joist cavities and foam in the edges. Man I love me some Thermax!

 

Or this.