New construction home structure & energy uses questions
I will be building my last house soon. I am in the construction supervision field and I would like to know if what I am contemplating sounds good. The home will be built in Chicago on a 1.3 acre lot with ½ wooded. The back of the house will face southwest for natural breezes. Here is the criteria I am contemplating during the pre-plan stage. The house will be around 2200 sq ft + a 3 car heated garage all with 8’ ceilings. The morning sun will be blocked by trees until around 10am and in the late afternoon.
ranch on a slab with 3’ foundation on a 12” footing, 2” Polystyrene R-10 foam attached to the inside of the foundation to top of foundation, fill most of the inside with gravel compacted to 95%, install 6 mil poly vapor barrier with 2’ overlaps under entire house & garage, 2” Polystyrene foam over gravel on entire house & garage, attach all hydronic heat piping directly to the foam board, pour 4” floor over the entire area with wire mesh, all domestic hot water copper pipe will be enclosed in foam pipe wrap with a loop and small slow moving circulating pump.
exterior wall & ceiling construction—1” poly-iso board on outside of 2×6 stud wall 16” o.c (so I can overhang foundation to cover 2” foam exposed), ½ cdx covering foam board so I can install brick veneer & vertical Reverse board & batten vinyl siding, 5.5” of cellulose, 5/8” drywall, no vapor barrier. The ceiling will be frames with ample room for 12” of insulation along the top plate, the attic will have adequate vent chutes & baffling, shingle over ridge vent, functioning gable vents, r-38 minimum blown in insulation. The garage door will be foam filled, the windows will be vinyl triple glazed with a foam filled frame and U value of around 17-20. We will caulk all the sill plates to the slab, foam around all windows and penetrations. I am contemplating using low density window foam inside the exterior electric boxes just to seal them up.
HVAC— Pvc duct installed under the slab around the perimeter for backup heat & central air hook to a 15seer a/c & natural gas 95% minimum furnace vented thru roof with pvc pipe separately, condensing boiler with numerous zones, the boiler would feed the indirect water heater. The boiler will be controlled by outside, inside, water temp controls.
Since we are both 58 y.o we are also installing 36” doors throughout the home along with wider hallways and larger bathrooms along with an open floor plan where possible, not making bathrooms and kitchen accessible but are considering options for cabinet placements. I am ordering extra 6” fillers to be used at sink and vanity in case of wheelchair in the future and vanities need to be removed.
If anybody can think of anything too add that will be cost effective please do.
Replies
There's some reason to question (based on ridge vent mfgr's recommendations) whether you should have the gable vents, especially in your climate.
You probably don't need housewrap with the foam on the outside, but you might want to consider it, for further air sealing.
It sounds like you will be sealing the heck out of the thing (which is good), but no mention of air exchange. You at least should provide space to retrofit a heat exchanger for ventilation, should you find that the air is "stale" inside (or that CO2 and humidity levels rise to high in winter).
But overall it sounds good.
Good catch on the vents. I prefer shingle over ridge vent and soffitt vents so i may get non functional vent on the gable. i actually dont like them either ever since I found a foot of powdery snow behind one in the attic about 20 years ago.
I am using house wrap but forgot to mention it.
I had made notes to discuss with my HVAC guy about adding an insulated duct tied from the outside soffitt to the return air duct with a damper on it so I could mix exterior air.
Thanks
Good catch on the vents. I prefer shingle over ridge vent and soffitt vents so i may get non functional vent on the gable. i actually dont like them either ever since I found a foot of powdery snow behind one in the attic about 20 years ago.
I am using house wrap but forgot to mention it.
I had made notes to discuss with my HVAC guy about adding an insulated duct tied from the outside soffitt to the return air duct with a damper on it so I could mix exterior air.
Thanks
Thing you probably have figured
but didn't make mention of:
Waterproofing, drainage and radon mitigation (if in your area).
I question the exterior foam which I think you mentioned on the outside of your foundation. Here, it's an ant attractor.
I may waterproof or damproof the foundation. I may install drain tile without a pump and pit. There is drainage ditches that I may run a trench from the footing to the high side bank of the ditch. there is 3' of fall in 75' to gravity drain the water accumulating around the foundation and remove the hydrostatic pressure. The foam in being installed on the inside face of the foundation from top of footing to bottom of stud wall. I had not woried about Radon since slab on grade.
Thanks
" I may waterproof or damproof "
The foam in being installed on the inside face of the foundation from top of footing to bottom of stud wall. I had not woried about Radon since slab on grade.
Sorry, misunderstood the part where you were hanging over the fondation-thought it was to get over exterior insulation.
And I do not know, but do assume that if Radon was a possibility in your area, that even w/o a basement there could be a way for it to infiltrate the living area from under the slab. I guess it's a question from me more than anything. Any concerns with a slab and radon?
If I had the ambition to build a house at this stage of life (I'm 60), I would do it just like you have described. Great plan.
Only one minor suggestion: Is there a practical way to have the supply duct system run above a false ceiling, possibly above a hallway where you could easily create a false ceiling, with high sidewall registers that would serve each space?
You would then have the best combination for heating (radiant floor) and cooling (supplies up high). You would also keep the ducts within the conditioned space. (Although, for cooling, which will be their primary function, underground ducts are possibly even more energy efficient as regards heat gain, but their air delivery is not as good.)
Floor registers for cooling are not nearly as efficient or comfortable as are those located near the ceiling.
The return air would be a single, central return with some kind of return air path from bedrooms--could be transfer grilles or jumper ducts, etc.
The ducted, dampered, outside air intake is a very good idea.
I was contemplating attic duct with urethan spray insulation. I was talked into underslab duct which will be easier to install and does not need insulation and much cheaper to install. I am putting the furnace only in the middle of the house in a closet for smaller duct size rather than way at the end of the house. Thanks for the help.
Since you are in the midwest and not building a basement, you might want to consider building one walk in closet or bathroom as a safe room / storm shelter. Tornados are not something you want to ride out in a normal above ground structure.
I have considered it and I am building a room 8x8 between the house & garage for the expensive utilities and our storm room. I am surrounding the room with 8" block with #5 vertical rebar in every core with a bent bar on top. I have some scavenged metal roof deck that I will lay over the top and support in the middle to carry the 4" concrete lid. I am tieing the #5 bent rods to each other with #5 bars on the roof. I am putting the well tank, softener, iron filter, electric service, boiler, all in the room. I am purchasing a commercial steel door and frame grouted during masonry I am adding a surface mount 4 point lock. I am installing an inswing door figuring that any debris from a tornado may cause us not to get out of the room if i had an outswing door. I was going to keep the ceiling low in there so the ceiling joists continue over the top of the room.
Thanks for the help
The exterior insulation may not be enough and will lead to problems later. Refer to this article for a comprehensive discussion:
file:///Users/jrp/Desktop/Jeff's%20Stuff/Construction%20Articles/Calculating%20the%20Minimum%20Thickness%20of%20Rigid%20Foam%20Sheathing%20%7C%20GreenBuildingAdvisor.com.webarchive
Also, the under slab insulation seems too thin. I used R-10 here in the PNW where our winters are relatively mild. I worry a bit that I should have used more.
I understood your description that domestic water will be routed through the slab in copper pipe wrapped in foam. If this is so, you must take great care to protect it and the wrap during concrete placement. Damage is likely and fixing it during the placement is very difficult. I'd use pex pipe and breath easier.
I assume you mean the exterior wall insulation but I am unsure if you mean the rigid 1" r-7.2 iso or the cellulose wall insulation r-21 to 22 or the 2" extruded polystyrene on the inside of the foundation. I feel that the r-10 underslab should be Ok considering I am using a full depth foundation 48" deep so that will stop the frost from getting to the floor. If you mean the exterior stud wall I feel comfortable with r-28 or so. I also need to consider the costs of increasing the r-factor and how many years it will take to get even.
I wish I could use PEX. The illinois plumbing code accepts it but the Local amendments have not adopted it. I would use PEX in a heartbeat if I could. I called the plumbing inspector and asked. The code as it is written says that nothing can be used to make the flow slower or decerease the pipe size. I said how about I oversize the pipe. He said great but you still cant reduce the size which will be done when you insrt the fitting inside and put on the clamp ring. I read the code and he was correct. In Indiana I always use PEX.
The copper & concrete issue should be simple. I am using the foam around the water pipe copper and an extra piece of foam over the foam where the floor pour is. The water pipes will also be pumped up with pressure on them and a guage on them. The hydronic heat is all pex tubing and will be encased in foam as it comes thru the top of the floor so no finishing tools nick it and that will all have pressure on it also.
Thanks
I was referring to the exterior poly iso foam. In any heating climate the foam on the exterior of the sheathing must be thick enough to prevent water vapor condensing on the interior face. Martin Holladay has written a lot of this. The link I provided doesn't seem to work. Here it is again. If this one doesn't work you'll have to search the Green Building site. Look for an article titled, "Calculating the Minimum Thickness of Rigid Foam Sheathing."
file:///Users/jrp/ /Jeff's Stuff/Construction Articles/Calculating the Minimum Thickness of Rigid Foam Sheathing | GreenBuildingAdvisor.com.webarchive
"I feel that the r-10
"I feel that the r-10 underslab should be Ok considering I am using a full depth foundation 48" deep so that will stop the frost from getting to the floor"
It isn't so much the exposure of the slab edges to frost conditions, but the fact that you will have a heated slab over cool ground throughout the year. A 2" foam layer would be fine otherwise, but the somewhat higher temperature of the slab and large area involved really push you toward 4" of foam under there.
Actually, with a highly insulated and tight home, the wisdom of spending the cash to have all that plumbing in the floor and in the flow center can be questioned. Many people like radiant floor heating for the "warm feet" feeling and what is perceived as the even distribution of heat. The feeling of warm feet won't be there unless the floor surface is in the upper 70s or higher, and that is fine for an older house, with lower levels of insulation and more air leakage, because the heat loss through the house's thermal boundary is so much higher than what you will have. As you have described the new house, the heat from a warm feeling slab will have little place to go, and the whole house quickly will become overheated. The slab temperature will have to be kept down to the low 70s to prevent overheating, and that just won't feel warm to bare feet, unless you have carpeting over the slab. But carpeting is an insulation layer, which you really don't want between the room and the heat source. Bottom line: you might reconsider the in-slab heat, and spend the money elsewhere.
A well designed external shell will give you a very low heat loss in winter, with few or no cold spots. In houses like this, you can pretty much put in any kind of heating system you want. It won't be very big. Moreover, the heat can be introduced almost anywhere and it will distribute itself quite nicely. Finally, the house will be much more isothermal than one with conventional construction. If you want the bedrooms to remain cooler for sleeping comfort, you'll have to keep the doors to those rooms closed.
[Edit:] On your exterior wall electrical boxes, there are boxes made for the purpose of air sealing easily. I used ones from Airfoil (www.airfoilinc.com). They come as single and double gang for walls, and round ones for ceilings. They have wide flanges for sealing to vapor retarder sheeting or drywall and foam compartments for filing with foam after wiring is run through them.
paul
There could be an affect of temp in a shower, if there was no pressure balancing valve.
So how does that affect your idea?
PEX use
It really is better to use PEX but I am in Chicago burbs and strong union here. I understand what is said here. The code says what it say. I know they are using the fact that fittings fit inside the tubing and therefore change the water pipe size. it does not make sense but those are the rules. We also only use pressure balanced valves here.
Thanks
I am almost ashamed to admit to being a plumber when I hear about such arbitrary, self-serving rules. This is nothing but corruption on a grand scale.
building a s
You have some good ideas but.
Visit http://www.buildingscience.com
Joe Lstiburek is the most knowledgeable guy in the world on how to build a house correctly. If your gonna do your last house then do it right the first time. Building Science will tell you how to build your house for the Chicago climate. That's mixed cold and hot you know.
Chas