Tight construction?

Chuck_7

I am working on a heating system for a large new house with plenty of windows.
I think I will assume it has "unusually tight construction" and provide a vent to outside for combustion air. On the other hand I think infiltration could be higher than I would figure using the window manufacturer's information on the window infiltration.
I do not usually work on residential. Can I count on the construction of a high end house to be tight?

Mark Eatherton1

Only...

if you get it in writing from the GC or the architect.

If you assume tight and they build it loose, and YOUR heating system doesn't keep THEIR house warm, who do you think a court of law is going to find in favor of...

If you get a letter from them stating they will build tight and they don't, you WILL win in court.

ME

Constantin

Like so many things, it depends.

For a tight home, I would always recommend a sealed combustion appliance, where possible. Usually, these come in the form of direct vent units that require up to two penetrations. Frequently, it's only one hole that has the two vents arranged in it concentrically.

As for the infiltration into the rest of the home, that's an educated guess right up to the point where the energy audit is performed and someone installs a blower door to see how your house does. For example, the best SIPS homes have almost no infiltration. The worst ones are just as bad as a regular stick-built home.

We foamed our exterior walls with 4" of corbond (older sections) and 6" of Icynene in the newer sections. Infiltration has dropped significantly as a result. However, I am less than impressed by the shoddy job the insulators did around our windows, as a single ½" bead of (admittedly expensive) low-expansion foam to seal the window seems somewhat pointless when the adjacent wall has 6" of Icynene in it.

I read in Home Energy today that there is considerable leeway as to what is and what isn't acceptable duct leakage. As far as the current EnergyStar program is concerned, even 16% leakage can still pass (!!!) in the ResNet program. Thus, if a tight house is your desire, put the requirements in writing before you start construction.

Only then will you have the cudgel to beat the GC if he/she does not meet the requirements of the contract with you rather than a seemingly arbitrary sets of regs that seem very flexible and hence useless in court.

Ron Schroeder_2

Expensive homes and tight construction can not be assumed. In fact, most of the worst insulated and high infiltration homes that I have ever seen have been over $500,000. Way to many expensive homes have been built for the looks and are pure junk under the drywall and trim. I you can't get documentation on the true construction quality, a blower door test would be a good idea.

Ron

Chuck_7

Not really a catch 22 but...In this case it is an oil boiler. If I assume tight construction, I may be able to get a direct vent oil fired boiler. If I assume the worst, I am too big for the direct vent ones I have seen.

joel_19

high end??

That depends on how you define high end. Here high end typically means house with 90k$ kitchens , walls of glass, completed finished media rooms that can cost 200k$ and.... the wind blows right through them , the quality sucks. Now we are doing a high end home right now that is very well built great windows and Icynene insulation . That one i clasify as "tight" but everything else is just blowin in the wind. How bad? last winter I saw pipes freeze in a house that where at least 15 ft from an outside wall. The house is valued at several million dollars. Money doesn't = quality in some cases.

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Unknown

Money = quality sometimes?

In fact, I'd say it's the opposite. The huge homes require large teams of people to build them and you inevitably get the "friday afternoon" syndrome where someone on the job just doesn't care and throws something together to get out early one day. It's just not the same as getting a good builder with a few assistants, or doing it yourself with some basic knowledge where you really care how it turns out.

ALL of the worst construction I've seen is on high end homes, and high end homes are the ONLY time I've ever been burned on a heat load calculation.

Specialty additions like Icynene are a different story, but if you're talking straight stick-built fiberglass, the insulation will slump, be packed in too tight, have gaps, the whole nine yards; guaranteed.

Pipe air in for the boilers anyway. But don't be shy with the infiltration estimate. I personally would guess in the .5-.75 ACH range for a high end home of unknown quality regular construction.

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Unknown

two stage, two boilers.

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Constantin

Good Points!

The issues you raise are precisely why I went with a small construction company and why I spend 2-3 hours on site per day, on average.

This exposed our current issues with the insulation folks, who installed inches of foam in the wall cavities but only put a thin bead (if that) around the window casings. Well, gentlemen, what's the point of insulating a Wall to R20 when the wind whistles just fine through the window casing? Argh.

I agree that many larger homes are built in what can only be called atrocious ways. However, I also think that some of the building permit requirements also play into the problem. That is, the McMansions around here are only allowed to have 2 levels or less. Thus, in order to get the interior playroom the McMansionites want, the houses spread out like pancake batter. Such an approach maximizes exterior surface area and hence creates plenty of area for infiltration.

Older large homes also don't look as much out of proportion precisely because they don't go off in 16 directions on only two levels. They tend to be more compact, taller, etc. and hence have less exterior surface area per unit volume on the inside. All things being equal, such houses will be easier to keep warm or cool.

Weezbo

many a good boilers gone south on PPconstruction.

a blower door test after the boilers in? hmmm......... on expensive home.....? well yah that could be a minor technicality..............better late than never i personally like nrt's idea..that way you have the chance to rotate boilers and add thier combined out puts if its needed.

Mike T., Swampeast MO

GREAT advice Mark!!!!

Personally, I don't believe it's possible to be too anal when it comes to insulation and weatherization. Unless there's an architect who will CERTIFY on the job or you're familiar with the builder's practice, assume "average" at best.

rich pickering

just out of curiosity, didn't the foam stop the infiltration? That is different than the r-value of the foam. Foam is usually airtight.

Constantin

That's the theory

However, foam is only airtight if it actually fills 100% of the perimeter around the window casings. If that is not the case, even a small leak can allow a lot of cold air to whistle through. In our case, there were gaps over 1/8" wide.

Plus, you never see foam advocates extolling the virtues of only needing ½" of foam to get a 6" wall to a R20 value. No, that cavity has to get filled. It's no different for the airspace around window casings and the like.

The trouble with infiltration and small holes is that they act like a thermal short circuit. The tighter the rest of the wall, the more egregious the effect of having a "short". Thermal transmissivity and all that.

That's why ResNet and other programs are trying to disallow the common practice of averaging wall cavity filling... a cavity whose surface is only covered to 75% is not going to average out to a 75% fill. Rather, the effects of open gaps and the like are going to drastically reduce the effectiveness of what insulation can be found inside the wall.

This is the main reason that fiberglass batts have to be cut very carefully to accomodate stud bays, piping, wiring, and the like. Otherwise, it's a lot of effort for naught. It's also a reason that other forms of insulation like dense-pack cellulose or foam are much more forgiving in terms of installation issues.

Mark Eatherton1

The problem with a blower door test after the fact...

is that you already have a "problem". Now you have more problems because the flue venting was installed assuming a different load requirement, and now you have to upsize the flue, which is NEVER an easy proposition.

The disadvantage of oversizing the system components based on a high infiltration estimate is that you will most probably have some short cycle issues at less than design conditions. Unless of course you were sharp enought to install a new sealed combustion, fully modulating appliance that can work around the load... Kinda hard to do with oil fired appliance though.

Sticky wicket to say the least. Catch 22 and all the other phrases you can come up with probalby apply.

The best phrase is C.Y.A.

If not, you may L.Y.A., L= Lose...

Happy Holiday Hydronicing!!!:-)

ME

Joe@buderus

Consider a chimney! Side wall/Direct vent of oil should be a last option. If the oil burner has any issue, plugged nozzle, set up issues, etc.., it will show on the side of the house and the nice landscaping. The possible odor smell, even if everything is done right can be an issue. Informed the homeowner/contractor about these issue's to protect yourself.

[Deleted User]

Infiltration

We are certified to do blower door testing, and usually get called in when the building won't heat or cool. It has always been the construction, not the equipment or sizing. By the time I get there and deliver the bad news, it is too late to to any real modification to the building. If I were doing a job, my quote would include my calculations for infiltration and insulation, with disclaimer that if actual construction does not meet those design parameters, they customer is in for more money, not the contractor. Don't get in a fight with the general contractor, let the homeowner do that...

Weezbo

Hello.....

when you do a blower door test ,with contractors who look for five star plus as thier standard, arent there many times the test shows they are even tighter than would be required even with that rating? granted there are alot of building "Practises" in vouge at present .for an example speak to us a momment about the Concrete in Foam buildings. or r 22 min walls with tremco +vapor barrier and tyveck,triple pane vynil windows ....seriously the quality contractor is going to be making the place like a hermetically sealed hyper tight building...

rich pickering

Got to love theory. I hope you showed somebody the error of their ways.

Bob Morrison_3

I would install the access to combustion air ...

Despite the many contrary examples, I would assume that the new construction is "tight" and install sufficient access to combustion air. That way you don't have to be concerned with estimating the infiltration rate. Install a motorized damper, end switching to enable the boiler, if you're concerned about an open duct to the outdoors. Of course, the more devices, the more complication...

Bob

ChrisL

Window perimeter foam

I was just foaming the perimeter of some newly installed windows the other day, and it clearly states on the window directions not to foam the cavity fully in depth. Now of course they don't say why that is, but with today's liability and all, would you expect anyone to do it differently?

ChrisL

Constantin

At the very least,

I would expect them to fill the cavity sufficiently to prevent infiltration. Leaving gaps around the casing is simply not acceptable.

Furthermore, Dow states on their web-site that the window and door version of their foam will not distort the window or door frame. I doubt that Dow would expose themselves to that sort of liability unless they were fairly certain that their foam wouldn't cause tons of trouble in the field.

Properly installed, you could probably even get away with the traditional "Great Stuff". It's a matter of knowing exactly how much the bead will expand post-application... tricky business at best.

Besides its low internal pressure, the other big benefit of the low-expansion PU foam is that the opposite surface will not encounter a skinned version of the expanding polyurethane (which is not as likely to stick and glue itself) as the stuff expands. Thus, I would always use low-expansion foam in a tight space.

jerry scharf_2

Two separate problems

I would never bet on infiltration giving you the combustion air you need. Just because it's coming through the walls doesn't mean it can be used by the boiler. You can even have situations where the wind can pull a leaky house into negative pressure (all depends where the most leaks are.)

The discussion about insulation and infiltration is a tough one as ME pointed out. Outguessing the GC's team on this is almost impossible. If you can walk around and see the insulation before you make the final boiler situation, all the better.

As for my view on insulation, it's all in the details. The idea that they would ever allow "fill averaging" is rediculous given the rough number that a 5% void can reduce insulation values up to 50%. It's all about details to get to a tight house.

I'm doing a complete foam job on my house. Foaming small cracks is really hard. I use low expansion foam (often Hilti) and probably get about 50+% fill on cracks more than 1/4". Beyond that it becomes a complete mess. On small cracks, it's caulk to seal and hoping for still air to give me R3 per inch. All the plates, trimmer studs and the like are vapor barrier taped

jerry