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Old 08-25-2019, 10:03 AM   #1
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Insulating Bonus Room w/gable question.....


Hello All,
I would like to add some additional insulation within the attic space above our bonus room and have a question on how much open air space to allow?


The attic space is really small. Maybe 15ft x 20.ft with a few feet of clearance. I'm thinking about laying down some paneling in in order to crawl in to perform the work.


1. I'd like to staple some radiant barrier to the rafters at a minimum. An opening will be allowed at the bottom of the rafters and the top for air circulation.


2. I'd then like to add some additional insulation to the attic floor. The question is how much can I add? It's a gable roof with a large "v" shaped gable vent at the end. So if I add a layer of r13 insulation, it may be cutting off some of the bottom of the gable vent. If I stop the insulation a few feet from the gable vent, thus allowing a cavity space, would the remaining open air space suffice?


I realize this isn't an easy question to answer but adding a layer of r13 would benefit the bonus room quite a bit. Otherwise, is there a thinner insulation, such as foam board, that you would recommend, etc? In addition, would it help to add a few roof vents (plastic louvers) for this tiny attic space area? The main structure is vented with use of two electric attic fans, btw. We have a hip roof, with exception of bonus room space, so it wasn't possible to utilize ridge vents.



Thanks,
Ralph
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Old 08-25-2019, 10:28 AM   #2
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Re: Insulating Bonus Room w/gable question.....


Do you have trusses? Were made as bonus room or attic storage trusses?
The difference is the amount of room they gave you for insulation on the sloped part of the ceiling. The rafter part in that area should be 2x19 or 2x12 so that you can have your insulation and 1 1.2" of clear venting above it, The vent you described makes it sound like insulation was never in the plan.
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Old 08-25-2019, 10:35 AM   #3
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Re: Insulating Bonus Room w/gable question.....


Yes, we have trusses. It has existing insulation now but I would like to add additional insulation because the room suffers from typical bonus room conditioning challenges.


Ralph
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Old 08-25-2019, 10:40 AM   #4
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Re: Insulating Bonus Room w/gable question.....


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Originally Posted by Ralph III View Post
Yes, we have trusses. It has existing insulation now but I would like to add additional insulation because the room suffers from typical bonus room conditioning challenges.


Ralph
Did you finish the room or was it done before you bought it?

The flat part of the ceiling is only about 20% of the ceiling so just adding there will not get you much relief,
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Old 08-25-2019, 04:21 PM   #5
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Re: Insulating Bonus Room w/gable question.....


Hey NealTW,


The bonus room was finished out at the time the home was built (1994) and was meant to be a part of the original living space. We purchased the home about a year ago.

You are essentially correct. The bonus room ceiling is slopped on two ends which represents about 55% of the ceiling. So the flat area of the ceiling represents about 45%. That part of the attic is difficult to access so I haven't been able to examine it closely. I assume they insulated the sloped rafters with use of rafter vents but cannot say for sure.

If they didn't insulate the slopped areas of the rafters then I will have to add rafter vents and insulation there. I will then add the radiant barrier to the upper part of the attic area which is exposed. Otherwise, I could run rafter vents and fully insulate the rafters? The later would cost more though but if that is a better plan (?) that is what I will do. Adding any amount of insulation to the attic floor will also benefit the area.

Anyhow, I am in the planning stages so your help is appreciated. I won't attempt to tackle this project until December or January when it is cool outdoors.


Thanks,
Ralph

Last edited by Ralph III; 08-25-2019 at 04:23 PM.
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Old 08-25-2019, 06:59 PM   #6
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Re: Insulating Bonus Room w/gable question.....


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Originally Posted by Ralph III View Post
Hey NealTW,


The bonus room was finished out at the time the home was built (1994) and was meant to be a part of the original living space. We purchased the home about a year ago.

You are essentially correct. The bonus room ceiling is slopped on two ends which represents about 55% of the ceiling. So the flat area of the ceiling represents about 45%. That part of the attic is difficult to access so I haven't been able to examine it closely. I assume they insulated the sloped rafters with use of rafter vents but cannot say for sure.

If they didn't insulate the slopped areas of the rafters then I will have to add rafter vents and insulation there. I will then add the radiant barrier to the upper part of the attic area which is exposed. Otherwise, I could run rafter vents and fully insulate the rafters? The later would cost more though but if that is a better plan (?) that is what I will do. Adding any amount of insulation to the attic floor will also benefit the area.

Anyhow, I am in the planning stages so your help is appreciated. I won't attempt to tackle this project until December or January when it is cool outdoors.


Thanks,
Ralph
So these are things you can look for that were not always done to todays standard.



In the side attics you want to check for blocking under the edge of the floor, that is mostly to stop conditions air from mixing with attic air.

The just next to that a 2x4 the would back the drywall and stop house air from mixing with attic air.

You can measure the the rafter size and should be able to put your hand above the wall to see if they added any depth above the room for more insulation.

And check if the walls are 2x4s or?

You should be able to see air chutes down to the soffet area and up to the upper attic.



Homework,, there will be a test.
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Old 08-25-2019, 10:16 PM   #7
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Re: Insulating Bonus Room w/gable question.....


Thanks Nealtw,


Your image isn't applicable because we do not have the side attic space. I have re-edited the image to depict exactly what type construction we have. I can only assume they insulated and used the rafter vents (air chutes) as shown. It will be a while before I can confirm exactly how they insulated the walls/attic slopes.



I'm considering adding the radiant barrier to the rafters in the open attic space and then adding additional insulation to the attic floor. I cannot say whether the additional insulation will partially block some of the gable vent though.


Ralph
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Old 08-25-2019, 10:25 PM   #8
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Re: Insulating Bonus Room w/gable question.....


Quote:
Originally Posted by Ralph III View Post
Thanks Nealtw,


Your image isn't applicable because we do not have the side attic space. I have re-edited the image to depict exactly what type construction we have. I can only assume they insulated and used the rafter vents (air chutes) as shown. It will be a while before I can confirm exactly how they insulated the walls/attic slopes.



I'm considering adding the radiant barrier to the rafters in the open attic space and then adding additional insulation to the attic floor. I cannot say whether the additional insulation will partially block some of the gable vent though.


Ralph
How do you know they are trusses,I ask because I have never seen trusses like that, That is what we see in balloon framing?
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Old 08-26-2019, 10:13 PM   #9
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Re: Insulating Bonus Room w/gable question.....


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Originally Posted by Nealtw View Post
How do you know they are trusses,I ask because I have never seen trusses like that, That is what we see in balloon framing?
Hey Nealtw,

They do make trusses as depicted in the image called "raised tie trusses". But no, I cannot say for sure that they are indeed pre-fab trusses minus closer inspection. Irrespective, I can confirm there is no side attic space.

I think I have a good plan in regards to adding radiant barrier and some additional insulation but I still have two hanging questions.

1) Is it going to be detrimental to cut off some of the gable vent? I think the additional layer of insulation would be more beneficial -vs- any slight loss of air flow from the gable vent but how much is acceptable? As noted, we have two electric attic fans that are used to remove the heat from the attic.

2) If I do end up causing a slight amount of air flow restriction would it be beneficial to add a couple of plastic attic vents for that part of the attic? At least some of the heat could be allowed to escape that part of the attic prior to the fans kicking on. Then when the fans kicked on, even if they drew some fresh air through the plastic attic vents, I do not see how that could be a negative? That would seem to compensate for any gable vent restriction?


God Bless,
Ralph
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Old 08-26-2019, 10:29 PM   #10
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Re: Insulating Bonus Room w/gable question.....


From the upper attic up close to the sheeting you should be able to see light above the insulation of the sloped part looking down toward the soffet. You always want more low vents than high vents or the attic will suck air out of the house.
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Old 09-18-2019, 10:01 PM   #11
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Re: Insulating Bonus Room w/gable question.....


With the limited thickness of a standard rafter, you may want to consider adding a layer of foam board before you sheetrock. It will add r-value, but more importantly reduce thermal bypass through the rafters. Here is model of the assembly with a ventilated channel, radiant barrier, fiberglass insulation, 3/4" foam insulation and drywall.
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