How to create a conditioned attic?

Question

My attic has reached the point of no return with storage. I must use it for that purpose. So now I have to find a way to insulate the attic's roof. For this DIY handyman dad, does anyone know of a step by step guide on how to convert an attic to a storage attic? I can imagine the steps, but I know I'm going to miss something crucial. I live in a normally cold area (New York State). Mentioning this since all articles I've read say I should aim to get R-60 if possible.

What I have:

1. since a bedroom was added above the garage, I have two attics (original + new) and they are connected.
2. the attic is triangular in shape (from outside), but rectagular attic floor (if that matters)
3. there is a ceiling vent (at the middle of the attic roof) to vent hot air?
4. there is an attic fan near the top of one side + a "window" cutout, where I guess its used for moisture ventilation.
5. the 'new' attic is for a cathedral ceiling, so I cannot walk on it, but I can see there is R-19 insulation (looks small in thickness, so R-value is an estimate).
6. There is insulation on the 'original' attic, but there are 2x6 planks used to hold all the storage
7. I'm fairly positive there are side vents since that area seems very dirty (wind?)
8. The 'original' attic roof does show nail points, so you can see there's nothing but lumber that I can physically touch.

My guess on what I would need to do:

1. Put hard foam (pink stuff) in between the beams - Im just not sure how to keep it on the roof?
2. close the 'window' + attic vent - somehow, since Im not sure.
3. close the connection between attics with a door, since I may still need access to that 'new' attic. And insulate that attic door Im putting in.
4. cover up all the pink foam with some vapor barrier, say 6mil plastic since it needs to face the 'living'/storage area. This is to keep an air seal.

I know there's something I've not considered. Does this look right to those that have done this? If there's any documentation with pictures I'd love to see it.

Answer 1

Ventilation

This is basically what you're trying to achieve, with respects to ventilation and insulation of the roof.

Soffit (eave) vents

Start at the bottom of the roof, with soffit vents.

Baffels

Baffels are used to provide a channel along the underside of the roof decking, to allow air to flow from the soffit to the roof vents. You don't necessarily need baffels, but you do want to provide at least one inch of free space under the roof decking. Baffles simply make providing this gap easier.

Roof Vents

You can use either pot vents, or a continuous ridge vent here.

^{Pot Vents}

^{Ridge Vent}

If you don't already have a ridge vent, you'll have to do a bit of work to install one.

• Remove the existing ridge cap shingles.
• Using a circular saw set to the appropriate depth, rip a straight line along both sides of the ridge.
• Install the ridge vent.
• Install ridge cap.

Insulation

Now that you have proper ventilation, it's time to think about keeping the conditioned air in the conditioned space. For this, you'll need insulation. If you used baffles in the previous step, insulating the roof is easy. If not, make sure you maintain a one inch gap below the roof decking while you install the insulation.

You can use whatever type of insulation you'd like, just make sure it will provide the R-value you want in the space available.

Vapor Barrier

Once the insulation is up, you'll want to install a vapor barrier to prevent any indoor moisture from getting up into the insulation. If moisture is allowed to get into the insulation, it could condense and cause mold problems and other water damage such as rot.

You'll want to use polyethylene sheeting, at least 4 mil thick. You're also going to want to seal all seams using house wrap tape, to ensure a good seal.

HVAC

Now that the space is sealed, it's ready to be conditioned. You'll have to install appropriate heating/cooling elements in the space, which completely depends on what type of heating/cooling you have. If you have forced air, don't forget the returns.

Carry the Load

The next item to address, is to make sure you and your stuff don't end up on the floor below. You'll want to make sure the floor of the attic is adequate to support the load. If it's not, you'll have to take steps to beef it up. For this, you might want to contact a structural engineer.

Access

Since you've been getting up and down to do all this work, I'm going to assume you have adequate access to the space. If not, you'll want to install a ladder, stairs, etc.

Answer 2

The first step is to make the floor designed to support a load. It's not unusual for an attic to be designed with only the materials needed to support the roof and hold up the drywall ceiling below. So you'll need to install proper floor joists, cross bracing, and then a subfloor. To get the joists in place, if there isn't a load bearing wall in the center, you may need to remove at least one side of the roof structure.

You need to insulate the underside of the roof. If this isn't done correctly, heat from the home can reach the underside of the roof, melt any snow, and after it runs down the roof where it refreezes on the colder overhangs. A closed cell spray foam is your best option since it won't mold if there's a leak and it allows no airflow. Second to that, I'd recommend a continuous air path from the soffit vents to a ridge vent along the underside of the roof. They make foam baffles that can be stapled in place for this. Then you can place any insulation you want over the baffle between the rafters. Check your location's guidelines for the appropriate R-value. You may need to sister a thicker rafter to give you the proper depth. The vapor barrier should face the inside of your home and you should make sure it connects to the vapor barrier running up the walls below.

A conditioned space needs an HVAC connection, so a vent needs to be run to the space (assuming you don't have a boiler). There needs to be an air path back to the return, so you either want an addition return or at least an opening in some wall that separates the attic from the rest of the home (you can cover that opening with a return grille. Make sure the HVAC vent being added doesn't exceed the capacity for the location you connect it to, and that the added conditioned space doesn't exceed the capacity of the overall HVAC system.