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New construction in Virginia - lots of questions


frankart's Avatar
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Join Date: Jan 2008
Posts: 52
VA

03-05-15, 10:17 AM   #1  
New construction in Virginia - lots of questions

I'm building a new house just outside of Richmond, VA. It will be about 2700 SF and mostly one level. The second floor is just a finished bonus room over the garage. The footprint of the house is not a nice rectangle. There are lots of bumps, books, etc creating a lot of corners and a lot of exterior walls area given the interior square footage. HVAC will be electric heat pump with propane backup. The entire house will be wrapped with DuPont Tyvek and finished with vinyl siding.

The question has come up about insulation and what we want to do. The builder pays for R-13 fiberglass batt insulation for the walls, R38 in the ceiling, and R19 in the floor. We have options. I really like the idea of the closed cell spray foam, but it's just not in the budget to do the whole house in closed cell foam.

One option I'm considering for the walls is 1/2" inch of closed cell foam topped off the 3 inches of blown cellulose. While the R-value does not increase significantly with this option, the sealing benefits of it seem to be a great compromise to me.

There is an option to add open cell foam in the attic for $5k.

In addition, the insulation contractor has quoted the pricing to do a conditioned crawlspace. Together with the closed cell foam and cellulose in the walls (and in the garage ceiling, under the bonus room), my price would be $4k.

Doubling the foam thickness to 1" and topping off the the blown cellulose more than doubles the price - almost $11k. I've asked why that went up so much. I'm waiting to hear back. In fact, I've sent a bunch of questions to both the builder and the insulation contractor, but I'm always looking for more opinions. If I may be so bold, I will post the questions here for discussion and recommendations.

1. Our current house was treated for termites prior to our ownership which consisted of the pest control company drilling a hole in one of the concrete blocks all the way around the foundation. How would something like this be accomplished if we had a conditioned crawlspace without destroying the integrity of the building envelope seal?

2. Will the heat pump need to be resized based on the increased volume of the conditioned crawlspace?

3. I understand the benefit of the conditioned crawlspace as it relates to capturing any duct leakage into the crawlspace...but the heat pump air handler unit will be in our attic and I think the duct work spiders out from there and feeds vents in the ceilings of each room. Aside from the moisture control benefits, what do we really gain since the air handler and ductwork is in the attic?

4. The way I understand it, the conditioned crawlspace will need an exhaust fan to keep it under negative pressure compared to the house. If this is the case, there is a constant draw of air from the living area into the crawl and then outside. We're constantly taking air that we've paid to heat, cool, condition, etc and throwing it outside. That seems like a big waste. What am I missing.

 
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XSleeper's Avatar
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NE

03-05-15, 11:21 AM   #2  
1). No termite expert, but when building a house, the termite treatment should be done in steps that are in conjunction with the construction of the house. Pretreatment of the soil prior to the concrete being laid, foundation being backfilled, after final grading, etc. Concrete blocks may be treated differently since the termites can tunnel up the hollow cores of the CMU. If your foundation is poured, I see no reason why they would drill any holes in it. Your local termite company will have the best advice based on their knowledge of the area.

2). Resized? Only if the conditioned space would make it undersized... if it is, then yes. The conditioned space is square footage just like any other room. However it need not be kept the same temperature as other rooms. I.E. the amount of ducting needed to make it "conditioned" will not necessarily be the same. Talk to your HVAC supplier.

3). What you gain is insulating the perimeter of the foundation instead of the entire floor structure of the house. Insulating and air sealing the perimeter is more effective than air sealing the entire floor, which is practically impossible.

4). The answer to that question depends on factors we can't really determine here. Conditioned crawlspaces can be successfully built which are not ventilated. The main reason to ventilate, as I understand it, is radon. If radon is not a known problem in your area, I would not ventilate the conditioned crawl space. As you mentioned, it would be a waste of energy. Ventilating the crawl space is simply a trade off... losing some energy for the sake of having less circulated air (in the form of your cold air returns) come from the crawlspace.

 
marksr's Avatar
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TN

03-05-15, 11:56 AM   #3  
When I was in fla where almost all new homes where built on slabs it was a requirement to treat the ground prior to the slab being poured. I don't recall any other termite treatment in new construction unless an infestation was discovered.


retired painter/contractor avid DIYer

 
calvert's Avatar
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Posts: 466
PA

03-05-15, 06:54 PM   #4  
I would agree that you should speak to a pest control company about the best local practice. Pre treating the soil prior to construction is a viable approach. One other approach may include the installation of a good old fashioned termite shield which may be in the form of aluminum or galvanized screening applied over the top of the foundation and extended out past the face plane of the sprayed foam. This prevents termites from building their tubes up the wall.

With regard to insulation, I would not spray just 1/2" of foam as this is not enough to prevent condensation from occurring. You need to have roughly 50% of the total wall r-value provided by the foam.

The issue of the bonus room over the garage could present heating and cooling concerns. Most frequently I hear complaints about cold rooms in similar construction. They are usually at the far end of a HVAC run and are getting the least flow of hot or cool air. You may want to make sure the system is designed to provide adequate flow to that room. You may want to beef up the insulation in that area as well by spray foam applied to the floor below and perhaps the sloped ceiling within that room.

 
calvert's Avatar
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PA

03-06-15, 04:28 AM   #5  
Something else that is frequently overlooked is duct sealing. All of the trunks and flex feeds in the attic should be properly attached to their respective infeed and outfeed points and sealed with joint cement and an appropriate foil tape.

I can't tell you how many attics I've been in where a section or more of flex duct became detached from the trunk and was pumping hot air into the attic.

 
Alisa K Kelley's Avatar
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03-11-15, 04:40 AM   #6  
I dealt with termites two years ago in my Virginia Beach home. I highly recommend that all of the soil a foot deep and a foot out be drenched in Termidor SC or the cheaper brand that has the exact same ingredients. I experimented with cheaper products under my shed and nothing else worked. I have not seen any termites or had an activity in the pop up activity detectors since trenching and drilling for Termidor. It's supposed to last ten years, it's 1/5 of the way.

 
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