Radiant Barrier in Attic

[dieselscout80]

We are thinking about installing a Radiant Barrier in our attic, but we are trying to determine if it's a good thing for us in South Carolina.

Has anyone installed a Radiant Barrier product in their attic?

How effective has it been in reducing your electric bill for AC during the heat of the summer?

Has the Radiant Barrier affected your cell phone reception in your house?

Do you feel it was cost affective?

Has it adversely affected your roof/shingles?

 

[WM75Guy]

We used TechShield for the decking on our house when we built in 2009 in East Texas and cut our cooling bill way down. The attic stays cool during the summer reducing the conduction of heat thru the insulation to the ceiling. The attic is usually no more than 10 degrees above the outside temp. We heat and cool 3200 square feet all electric and the auto season thermostats are set for 68 - 72 degrees year round. Our electric bill has at the most been $350 during the hottest part of the summer. Between the house and the stables there are 3 AC heat pumps, 1 3 1/2 ton, 1 2 1/2 ton and 1 2 ton, 4 refrigerators and 3 hot water heaters. Our old house at 2200 square feet with 1 5 ton HVAC heat pump, 1 hot water heater, and 2 refrigerators and no TechShield used the same or more electricity and I could not keep the house cool. The best we could do was 78 degrees during the hottest part of the summer.

 

[ustmd]

We are thinking about installing a Radiant Barrier in our attic, but we are trying to determine if it's a good thing for us in South Carolina.

Has anyone installed a Radiant Barrier product in their attic?

How effective has it been in reducing your electric bill for AC during the heat of the summer?

Has the Radiant Barrier affected your cell phone reception in your house?

Do you feel it was cost affective?

Has it adversely affected your roof/shingles?

I used it on my shop and the tack room--I asked for it on the house, but the builder "forgot". I would highly recommend it. It is very common here and there are talking about making it part of the code for the city of Austin.

 

[DKCDKC]

My last house was built in 1974 with the then-popular all aluminum insulation - just layers of aluminum foil and brown paper. It actually worked for the summer in central Virginia, but failed miserably in the winter. And it never affected cell phones. Of course the house also had aluminum wiring. That was a blast.

My house now is mostly shaded by oaks. That works too.

 

[dieselscout80]

My last house was built in 1974 with the then-popular all aluminum insulation - just layers of aluminum foil and brown paper. It actually worked for the summer in central Virginia, but failed miserably in the winter. And it never affected cell phones. Of course the house also had aluminum wiring. That was a blast.

My house now is mostly shaded by oaks. That works too.

Thanks guys!

If you have a Radiant Barrier that is stapled to the bottom of the rafters is it solid from the bottom to the top or is there a gap at the bottom and top?

We had a nice big Oak tree that keep the morning sun off hte east facing side of the house, but it rotted from the inside and fell down in a wind storm at least it missed the house.

 

[edlegault]

Wouldn't regular insulation (batts or blown in) be a better barrier?

 

[wcampbell47]

The house we built last year has a radiant barrier on the bottom side of the roof decking. Traditional bat insulation was installed as well. In the summer months my electric bill was never over $200 so I think it helped a lot. Radiant Barrier has the potential to reduce your cell phone signal.

 

[dieselscout80]

Wouldn't regular insulation (batts or blown in) be a better barrier?

I have about 14" to 16" of insulation currently in the attic floor.

 

[SPIKER]

I believe you need to
1. insulate the inside from the outside attic space (attic floor) with or without wood flooring makes a difference. With wood insulate between drywall living space and wood floor with blown in insulation. In this case the radiant barrier can be stapled to the rafters so there is free space between the floor and radiant barrier. You need to have full length peak venting so air can come up from the eves and under the roof above radiant barrier and out the peak vent. If you have copulas or attic vents they need to pull out this heated air.

2. with NO attic Floor but lots of blown in insulation you can lay the radian barrier right on top of the insulation on the attic floor. This is a bit of a better solution but stops the attic as storage space which is needed in many homes. The roof venting is still needed in either case but a powered or solar vent in this case works much better. You can also re-insulate over blow more insulation on top of the radiant foil stuff as well later on.

It should not make a difference in cell reception unless you have the exterior walls insulated with radiant barrier as well. But I have no claim on this aspect.

Mark

 

[dieselscout80]

I believe you need to
1. insulate the inside from the outside attic space (attic floor) with or without wood flooring makes a difference. With wood insulate between drywall living space and wood floor with blown in insulation. In this case the radiant barrier can be stapled to the rafters so there is free space between the floor and radiant barrier. You need to have full length peak venting so air can come up from the eves and under the roof above radiant barrier and out the peak vent. If you have copulas or attic vents they need to pull out this heated air.

2. with NO attic Floor but lots of blown in insulation you can lay the radian barrier right on top of the insulation on the attic floor. This is a bit of a better solution but stops the attic as storage space which is needed in many homes. The roof venting is still needed in either case but a powered or solar vent in this case works much better. You can also re-insulate over blow more insulation on top of the radiant foil stuff as well later on.

It should not make a difference in cell reception unless you have the exterior walls insulated with radiant barrier as well. But I have no claim on this aspect.

Mark

We have a partially floored attic and will be flooring more of it. Our attic also has a full length ridge vent and soffit vents that are unblocked to allow air flow. I'm not sure whats under the vinyl, but I doubt there is a radiant barrier the home was built in 1989.

I'm thinking that I should start the radiant barrier about a foot above the insulation and end it about 18" or so before the ridge vent does that sound ok?

 

[ustmd]

We have a partially floored attic and will be flooring more of it. Our attic also has a full length ridge vent and soffit vents that are unblocked to allow air flow. I'm not sure whats under the vinyl, but I doubt there is a radiant barrier the home was built in 1989.

I'm thinking that I should start the radiant barrier about a foot above the insulation and end it about 18" or so before the ridge vent does that sound ok?

Yes--that is what we did

One thing--stable well. If you have good air flow through the attic, over time, the stables can rip out

 

[dieselscout80]

Yes--that is what we did

One thing--stable well. If you have good air flow through the attic, over time, the stables can rip out

I wonder if those capped nails they use for house wrap would be good to use or a strip of wood with nails or screws?

 

[SPIKER]

One thing if you have ridge vents AND side vents on the sides of them then you could run the Radiant barrier up and over the peak and back down the other side. you would need a flat across the peak so there is opening lengthwise between ALL of the trusses this will bring the HOT air up to the peak and out the vent NOT into the attic space like it would if there is an opening back into the attic space.

The SIDE vents will then pull in enough cool air into the space under the radiant insulation to keep that space conditioned to meet outside temps better. the radiant is reflecting much of the heat waves back out towards the roof and space BUT it will also warm up the underside of the roof causing convection heating (air pulls up from bottom and out top if it open to the room.

Mark

 

[dieselscout80]

One thing if you have ridge vents AND side vents on the sides of them then you could run the Radiant barrier up and over the peak and back down the other side. you would need a flat across the peak so there is opening lengthwise between ALL of the trusses this will bring the HOT air up to the peak and out the vent NOT into the attic space like it would if there is an opening back into the attic space.

The SIDE vents will then pull in enough cool air into the space under the radiant insulation to keep that space conditioned to meet outside temps better. the radiant is reflecting much of the heat waves back out towards the roof and space BUT it will also warm up the underside of the roof causing convection heating (air pulls up from bottom and out top if it open to the room.

Mark

When you say side vents are you refering to vents in the soffit?

If you are then yes I have soffit vents, a full length ridge vent and gable vents at both ends of the peak of the roof.

 

[CornReaper]

When your house has a ridge and soffit vent as explained in the scenario above, you should not run the insulation all the way down to eaves and across the ridge. You will impede or could impede the natural air exchange, the whole reason to have the vents in the first place. Stop the insulation about 8" away from the eaves or insulation if you have any and the same distance from the ridge. If you don't have ridge/soffits you can run the insulation up and down the rafters with no breaks. Hopefully you have louvres or something to allow some air exchange. In most cases use the perforated product, tiny pinholes, to allow moisture transfer. For your barn insulation, there is another type of radiant barrier with cellular construction (thickness) that will give you an R-Value as well. This material is solid. Installing it gives you a vapor barrier and will slow or eliminate condensation in your out buildings.

 

[dieselscout80]

When your house has a ridge and soffit vent as explained in the scenario above, you should not run the insulation all the way down to eaves and across the ridge. You will impede or could impede the natural air exchange, the whole reason to have the vents in the first place. Stop the insulation about 8" away from the eaves or insulation if you have any and the same distance from the ridge. If you don't have ridge/soffits you can run the insulation up and down the rafters with no breaks. Hopefully you have louvres or something to allow some air exchange. In most cases use the perforated product, tiny pinholes, to allow moisture transfer. For your barn insulation, there is another type of radiant barrier with cellular construction (thickness) that will give you an R-Value as well. This material is solid. Installing it gives you a vapor barrier and will slow or eliminate condensation in your out buildings.

I'm not going to put insluation just a radiant barrier.

 

[Gary Fowler]

A radiant barrier will help with attic temperatures during the summer but without some ceiling insulation it wont be enough to keep you cool in summer or warm in winter. I have the radiant barrier in the ceiling of my shop plus bat insulation between the rafters and in the walls and the mylar radiant barrier on top of the insulation. In my house, I have the same but with bat insulation between the rafters, then 12-18" of blown in fiberglass on top of that then the mylar film radiant barrier on top of the blown in insulation. The roof has radiant barrier full length from center ridge vent to soffit eaves.
You can see in the second photo how the front porch has it installed also in total roof area and walls. This actually went on first then the roof decking on top of it.
My shop just has 8" bat in walls and ceiling and of course the roof radiant barrier with the mylar radiant layed loosely on top of the bat insulation. This was an after build scheme that we went for in hopes of saving additional energy costs. Not sure if it is helping much more than than just the barrier and insulation and it was super costly. Possibly I should have just invested in more insulation for the cost. Insulation is cheap compared to energy cost.
My shop does pretty well with what it has and stays above freezing with no heat and comfortable with a 1500 watt heater running during winter and that only runs part time. Summer time, I can cool the whole thing to a comfortable 80F with a 14,000 BTU window unit.

 

[crbr]

Thanks for the pictures

 

[SPIKER]

With the Soffit and Gable Vents then you can run the radian barrier from attic floor to peak & back to floor. the Peak should have a free air space below the peak vents so all the rafters can get a common airspace. Seal up the airspace between the roof and the attic to prevent thermal transfer via convection. the heat trapped between the roof and the radiant insulation will escape thru the peak vent & replaced by the air coming in under the sides & soffit. The Gable Vents should be enough for for the attic if not you may need a powered solar type vent in one of them on the south side to pull air out, same for near the peak in the roof a powered solar type would help a lot. \

Mark