Duct insulation in the Crawlspace

If you are involved with building a house, you will encounter challenges that you never thought could exist. You will think to yourself, "How can this be so difficult?" And when you try to figure out how to insulate a crawlspace and the ducts that run through it, you will be especially challenged. 

Remember one of the highest priorities in building John's house is to make it energy efficient. That means you try to minimize the energy losses from the home's shell, the thermal envelope. And that includes every side of the house including the dreaded crawlspace. Now we made the crawlspace a little less disgusting (dark and dank and spidery) because we did not enclose it. The house's foundation is on piers. So the space is open to the outside. I designed it that way because the house is very near a pond and a large creek and there is potential for flooding.  We had a torrential rainstorm 2-3 years ago that flooded most of the yard, it did not come to the area where the house is located. Still I thought it was prudent to build on piers to eliminate that potential problem.

We have insulated most of the joist bays in the crawlspace, but now we have insulate around the ducts. The ducts are already wrapped with what is listed as R-8 fiberglass though I don't believe it is truly R-8. If you google R-8 HVAC duct wrap you will see various products that are used to wrap ducts. These products are generally 2 inches thick and have foil-faced layer that is taped around the ducts. In order for the insulation to truly have that R-value (resistance to heat transfer) it cannot be compressed. It must be 2 inches thick, but you really can't wrap and tape it around the ducts and preserve that 2 inch space. It is usually compressed to about 1 inch which gives you at best an R-value of 4. I think that is much more realistic. 

You can see where I reinforced the taping on the duct insulation and how it compresses the insulation surrounding the ducts. I've made sure there are NO air leaks in the insulation surrounding the ducts. 

So here's the situation, you've got a house with the roof insulated > R-50, walls insulated > R-30, floors insulated >R-30 and your crawlspace ducts are insulated at R-4? Are you kidding me? That drives me crazy. I just can't see leaving them like that. So we are encapsulating the ducts in 1-2 layers of polyisocyanurate foam boards which will triple the effective R-value surrounding the ducts. It will not likely equal the insulating on the floor, but it will be close to R-20. 

This post aims to show you some of the details of enclosing the ducts. It is tedious work, not as itchy as working with the batt insulation. I hope I can explain these details so that they make sense. 

This photo demonstrates 3 things:

1. The joist bay is air sealed at the edges with Prosoco Joint and Seam filler so air from one bay cannot move from one joist bay to another.

2. The duct is very well air sealed to the subfloor.

3. We have a 2x4 in front of the duct which is to help with placement of the foam board which will enclose the duct. 

Back view of the same duct, now surrounded by polyiso foam boards.

Ok, this is view shows the same duct after we've applied the foam board onto the front. The foam board is glued on with construction adhesive, then foamed around the edges. Also the front of the board is taped to the subfloor and joist bays. So the likelihood of leakage around the foam boards is very low. 

You can see where we have installed some more boards around the duct and the joists. There will be longer boards parallel to the ducts on each side and underneath. Again, all the edges between the boards will be foamed and taped as well as I possibly can manage. This was a slightly more difficult duct because it had to dip down around the rim joist from the main part of the house and back up to the porch. It is the only duct in the enclosed porch which is just 8' x 16'. 

I'm off again tomorrow so I should be finished with this duct then. I hope this is helpful for someone working on their house. Good luck. 

Crawlspace Insulation

Crawlspace insulation under enclosed porch

The current project on the perpetual house (perpetual building mode, that is) is insulating the crawlspace. Anything in a crawlspace is a pain, but insulating in a crawlspace is particularly painful - insulation in your eyes, breathing insulation, insulation on your skin, etc, etc. I wear a mask, glasses and a Tyvek suit to make it a little less onerous.

We are doing this ourselves because we can and our labor is free. We is me and Rich, my brother-in-law. Also I believe that no one else will do the same quality work. I don't know that to be true, but I suspect it is true based on the insulation work I've seen done in the past by others and the fact that no one else cares as much as I do and no one else is as willing to do this painful job as I am.

Ok, so here is the plan for insulating under the porch - the floor joists are 8" which works out to a 7.5" space for insulation. I have 2 different kinds of insulation that could be used for this area: -
5.5" Roxul mineral wool insulation which is listed as R-23
2" Roxul Rockboard insulation (about R-8).

For the 7.5" space, we installed the 5.5" Roxul first and the 2" Rockboard to finish filling up  the joist bay. The 5.5' Roxul batts were easy to apply, but the 2 ft wide Rockboard was a pain. We had to cut it to fit each of the floor bays which ranged from 21" to 23" wide. Then we had to wedge that stuff in. It was awful. I don't find Roxul to be as horribly itchy as fiberglass, but it does aggravate me, especially when I have to wedge it in with my shoulder and the stuff is going down my neck. Some of it was a little loose so we put strapping across it to hold it until I install the DA vapor permeable membrane from 475 Building Supply.

Larger view of the crawlspace insulation under the enclosed porch. Strapping is to hold it in place until the DA vapor permeable membrane is installed by stapling it to the floor joists. 

Lynn warned me about critters under the house, but other than the Carolina Wren nesting on one of the piers that we are having to work around, and an occasional wasp, critters have not been a problem. There is a dead critter present though. You might be able to see on the pier on your right. See the close-up below.

A little dead bat. I keep meaning to take it down, but I really don't want to touch it even with gloves on. 

I have to fill 2-3 small gaps where we did not abut the Roxul Rockboard together very well and I need to foam the gap between the floor joists which you can see above the bat. That is the space between an open part of the porch and the area below the door to the enclosed porch. 

Well, that's where we are today. I am off tomorrow so I will work on insulating the rest of the floor under the house. It is forecasted to be a tiny bit cooler tomorrow - in other words, it is not supposed to reach 90 tomorrow. Little blessings. Thank you for reading.

Extreme Air Sealing - the Crawlspace Edition

Air sealing the duct work to the subfloor. The interior side of the duct work is taped as well. I like redundancy in air sealed layers.

As any regular readers of this blog will know (assuming there are regular readers of this blog outside of my friend, Lynn), I am crazy obsessed with air sealing. After studying how to build an energy efficient home over the past 4 years, this is clearly the most important first step in that direction. Also it happens to be something I can actually do. You don't have to measure or cut precisely, you just have to crawl or climb around to awkward places to squirt foam, goo or tape any and every potential opening in your thermal envelope - the separation between inside and outside. I am capable of doing that.

The last step in air sealing this house is sealing the duct work and connections in the crawlspace. I don't know if John's house technically has what you call a crawlspace because it is built on piers and the space is open to the outside, but it seems like a crawlspace when you have to crawl and duck floor joists for hours at a time.

As I noted in an April post, the HVAC ducts are sealed with some kind of DUCK tape which really doesn't hold well for any length of time - meaning for years of the usefulness of the duct work. I did not take off all the fiberglass insulation and re-tape the ducts with a more long-lasting tape. I just could not make myself do that, but I did reinforce EVERY SINGLE JOINT and EVERY SINGLE PIECE of DUCK TAPE with a very adherent and long-lasting tape, mostly Siga Wigluv. I am hoping that the ducts are so well encased that they won't move much and the tape underneath the fiberglass insulation sheets holding the ducts together will last better.

This tape has only been on for a couple of months and is already loosening. You can see here I have reinforced other areas with Siga Wigluv. I did that on every duct.

This is another example:

You can see all the little strips of paper from taping the pipes.

After the sealing is complete, then I will insulate the 9.25" joist bays with 2 layers of Roxul Mineral Wool insulation - 5.5" layer and a 3.5" layer. The ducts themselves will be encased in the leftover polyisocyanurate foam which you see on your left. I haven't figured all those details for insulating around the ducts yet. 

Rich finished the interior painting, John is building bathroom vanities and I am crawling around underneath the house, sneezing like crazy - air sealing which is what I do best. That's where we are today.

We GOT the construction loan!!

Just a brief message to say that we signed for the construction loan yesterday. Finally. Now we can finish this house. John is extremely happy about it.

Ok, here is a brief list of what we need to do to finish the house.

1. Rich to finish interior painting
2. Air sealing the crawlspace (covered in the next post)
3. Insulate the crawlspace
4. Inspection so we can get power to the house.
5. Install HVAC.
6. Re-sand the floors because we kind of messed them up with the recent work
7. Stain the floors
8. Apply Waterlox finish to the floors
9. Baseboard trim and wainscoting downstairs.
10. Tile bathroom floors
11. Tile downstairs shower
12. Tile around upstairs tub
13. John to build vanities for both bathrooms
14. Install bathroom vanities
15. Install plumbing fixtures, sinks, hot water heater, etc.
16. Install electrical outlets, lights, fans, etc.
17. Paint exterior
18. Stain porches
19. Termite treatment
20. Get certificate of occupancy
21. Move John into his home

I've probably forgotten a lot of stuff, but that's gives you a rough idea of what we need to do.