# Condensation With A Tight Envelope



## WNYcarpenter (Mar 2, 2007)

Last year we built a home with SIPS panels, and closed cell insulation. Everything is sealed tight. (pagoda project)

This is a vacation home that runs year round in a cold climate. There is little to no traffic. We are in and out periodically for punch and winter surveillance and We've found a pretty major condensation problem. Mostly at the windows and doors....We've been monitoring this for a couple months now, and there is no clear answer.

The home has an open floor plan (2000 sq ft.), with the only heat being radiant under the first floor. I'm guessing the heat is set at about 55* +/-. 

The air exchange is with a simple open air vent that functions with a pull string. (that confuses me....why did we seal everything, then put a hole in the wall?)...just like cracking a window.........and a fart fan that continuously runs.

During building, the structure was exposed to a lot of weather. I posted a thread last winter as we had some issues just before insulation. I didn't have any luck digging out that thread, but, everything was wet...I never kept track, but we did remove a considerable amount of moisture before insulation and DW.

This house has been through a summer season (little to no use), and now is seeing it's 1st winter.

Are we still pulling water out of the structure? There are no blemishes to DW or woodwork.......is it the lack of traffic/air exchange? The difference in r-value with the windows?

For now, we have a dehumidifier running....

any thoughts?


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## loneframer (Feb 13, 2009)

Moisture will always condense on the coldest part of the exterior wall during the heating season. The fact that you have radiant heat reduces the amount of moisture removed by say a forced hot air system. (dry heat) Not as much circulation as a forced air system to help carry the moisture away either.

I know people who paid to have a humidifier installed on their FHA system, only to have to render it inoperable because of condensation on the glass.

To my knowledge, the only way to reduce the amount of condensation on the glass is to reduce the amount of humidity in the house.:thumbsup:


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## SLSTech (Sep 13, 2008)

or raise the heat inside - the colder the air the less moisture it can hold

Is this house on a lake / high humid area? Basement, Crawl or Slab - how was it finished? The continuously running fan can add to the moisture, especially if the makeup air is being pulled in from a humid area. 

Was a blower door used to see how leaky the house is / if the fan is needed / or how much is needed to hit ASHRAE's .35 mark? If needed you might consider adding a timer or better yet an HRV/ERV on a timer to help prevent pulling in more air than needed


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## Morning Wood (Jan 12, 2008)

You probably should have installed a air/air heat exchanger if the house is really that tight. What you have with the fart fan is useless in my opinion. I would run humidifier for a while and see what happens. I think you could still be drying out. How good are the windows you put in?


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## loneframer (Feb 13, 2009)

With SIPs and closed cell insulation, any moisture inside is going to stay inside, with little help from a fart fan.

The glass will always be the coldest part of the building envelope and condensation will always form on the warm side of it.

Either lower the humidity in the house, drop the thermostat substantially, or a combination of both.:thumbsup:


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## SLSTech (Sep 13, 2008)

MW - a humidifier as in add more moisture? sure you didn't mean dehumidifier?

Lone - lowering the temperature of the house means the air can not hold as much moisture causing further condensation when it makes contact with an area that is cold enough that it reaches full saturation / 100 RH / aka the dew point 

Now I am assuming that they do have double paned windows & everything was built really well based on who is asking the question - thus raising the temperature some should help warm the windows up enough to help prevent it from forming while the house dries out. (Not to mention that it is a radiant floor system which heats a building a totally different way)


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## loneframer (Feb 13, 2009)

SLSTech said:


> MW - a humidifier as in add more moisture? sure you didn't mean dehumidifier?
> 
> Lone - lowering the temperature of the house means the air can not hold as much moisture causing further condensation when it makes contact with an area that is cold enough that it reaches full saturation / 100 RH / aka the dew point
> 
> Now I am assuming that they do have double paned windows & everything was built really well based on who is asking the question - thus raising the temperature some should help warm the windows up enough to help prevent it from forming while the house dries out. (Not to mention that it is a radiant floor system which heats a building a totally different way)


 You may be right about lowering the thermostat. In my mind, I was thinking that the warmer air is carrying more moisture, thus allowing more of an opportunity for condensation. I have to wonder if temperature differential plays a role as well.

Anyway, the tighter the envelope, the more complicated Building Science seems to be.

There must be balance between insulation and ventilation.


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## nailkiller1 (Jan 15, 2009)

The problems with your house needs to be treated mechanically
A competent hvac guy could resolve your problems

A tight envelope simplifies the problem in my mind
All the air is to be treated mechanically
Your equipment is either not working properly
or you are in need of more equipment


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## SLSTech (Sep 13, 2008)

loneframer said:


> You may be right about lowering the thermostat. In my mind, I was thinking that the warmer air is carrying more moisture, thus allowing more of an opportunity for condensation. I have to wonder if temperature differential plays a role as well.


No worries, but you might want to check out a Psychrometric chart if you are still doubting --- in his case @ 55 inside the air can only hold 63 grains of water per pound, while @ 65 it could hold 90 grains before condensing / reaching dew point

The catch is not how much it is is holding but at what point condensation / dew point is reached in this case

Seeing he has a radiant floor heater, well the temperature at the window level is also probably lower (compared to a normal system) so the amount of water is probably a lot less than shown above



loneframer said:


> Anyway, the tighter the envelope, the more complicated Building Science seems to be.


Yes & no - the numbers and manuals have been out for years, but many people simply ignored them & went with rules of the thumb --- Build it Tight and Ventilate it Right (get a HVAC guy that runs the numbers properly using the manuals J, S, T, & D - consider getting a blower door test done, to find out how much ventilation really needs to be brought in)



loneframer said:


> There must be balance between insulation and ventilation.


 The catch is not the insulation value, but is the proper system used, is it sized properly and how the house was built...

For example on the house and moisture, was it built during the rainy season / wet materials, did we allow it to dry out and verify it before installing the insulation, the drywall or flooring? Do you know how much water vapor is released when installing OC Foam, or cellulose, not including the drywall or tile? Did we use propane heaters to help warm the place which also pumps out tons of moisture as a by product?

The reason I use some of those for examples above is a problem house on another site - wood floor 7.5 - joist 8.5 - subflooring 19% (Guess what was wet as a spounge when the wood was installed & guess what is now cupping big time when the AC was turned on - Oops)


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## nailkiller1 (Jan 15, 2009)

I had a light problem with moisture in a house two years ago

All the equipment was checked five different times every time checked out to be working properly

The hvac guy was making up all kinds of excuses 
(to many showers, fans need to be on blah blah blah)
What I finally did was told the hvac man we need a bigger air exchanger
(Major guess)

He said no way
I ended up buying a bigger air exchanger on the premise that if it worked the heating guy would pay for it
Installed one day
all the moisture was gone the next day


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## WNYcarpenter (Mar 2, 2007)

Thanks, good stuff:thumbsup:.

Full basement, ICF, with a slab over a vapor barrier.....sump pit...Pella designer windows, custom wood doors.

We have not tested the performance of the envelope.... I'll have to do some research 'cause I've never heard of ASHRAES .35.

This is definitely the direction all of our homes are heading....especially in WNY. I don't think we (my company) understands the system as well as we thought.

The year before, we used a heat exchanger.....it wasn't SIPS, but it was a step towards 'advanced' framing. The difference is that we heated with a UNICO system......I was asking about that, and I was told the with radiant heat you don't need the return air....

Are we still pulling moisture out of the structure? Is that why the air is so humid?.....
My concern is that once everything dries out, it will shrink and the whole project will turn to sh!t.....To date, everything looks good. No nail pops, miters and joints are holding, flooring is perfect.


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## katoman (Apr 26, 2009)

I agree with Nailkiller.

We built the first "energy star" homes here in Ontario. Sealed tight. We installed HRV systems which need to be properly installed and sized to the house.

But you have radiant heating. I don't have an answer for that, other than as nailkiller stated, you need to mechanicaly treat the air.

Think of the house as living in a plastic bag. I'm presently working in one of the homes we built, the HO is very fussy about humidity and temp control. 

This house has forced air heat, HRV, humidifier, and a de-humidifier. The humidity and temp is controlled with these systems.

But you need a mechanical guy who really knows his stuff. Not that easy to find.

A typical poured conc. foundation takes a year to a year and a half to completely dry out. That is for all the water to be drawn out of it.

But I think (and I'm no expert) you have a basic design problem here. You don't have a mechanical method to move and de-humidify the air. That would be the solution IMO.


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## CStanford (Feb 5, 2010)

WNYcarpenter said:


> Last year we built a home with SIPS panels, and closed cell insulation. Everything is sealed tight. (pagoda project)
> 
> This is a vacation home that runs year round in a cold climate. There is little to no traffic. We are in and out periodically for punch and winter surveillance and We've found a pretty major condensation problem. Mostly at the windows and doors....We've been monitoring this for a couple months now, and there is no clear answer.
> 
> ...


Turn the heat up, crack a couple or three windows. Works every time.


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## ENERGYSTAR (Oct 17, 2010)

How close is the open vent/hole to the fart fan? With no means of circulating the dry air you are bringing in, it may be a waste of time. Using ICFs is a big expense, you should spring for the extra $1000 and install a decent HRV. ASHRAE 62.2 states that you need 0.01 cfm for every square foot and 7.5 cfm per bedroom+1 of continuous ventilation. If the place is 3 bedrooms this is a total of 50 cfm, or that of your average fart fan. 

Perhaps a better solution would be to simply plug the inlet and let the fan draw air in from wherever it can, which would serve to distribute the incoming air and improve circulation. The problem is that your fart fan may not be able to move 50 cfm out of this tight envelope. You might have your HVAC guy check it with an anemometer.

A new home can hold a ton of moisture for the first year in drywall and concrete. You should monitor the humidity closely. The first tight home I built was 4300 sq.ft. with only 2 people living there. I set it up for an HRV but did not install the unit thinking that the occupants could not generate enough humidity in that large of a space. Two months later it dropped to 10 degrees and the inside humidity was 50%. There was a river of water flowing down each window, which were Pella Designer series by the way, and there was rain coming down the vent hood onto the cook top. After I hooked up the HRV, the interior humidity dropped to 35% in just 8 hours.


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## jeffatsquan (Mar 16, 2009)

If a heat recovery ventilator wasn't part of the design criteria 

I would be looking for a new designer


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## WNYcarpenter (Mar 2, 2007)

jeffatsquan said:


> If a heat recovery ventilator wasn't part of the design criteria
> 
> I would be looking for a new designer


I wish it was that easy. Sometimes the PM outsmarts himself, but This project was a first for us. He does 90% of the research, and to his credit, he's good. However he can be a bit pretentious. He gets what he wants, and has been known to step over a dollar to pick a dime.

With a new system like this, I'll give him the benefit of the doubt. We might spend 40 man hours trying various fixes before ultimately going to an HRV system that should have been in place from the beginning, or he has a better understanding than I'm giving him credit for. 

Explaining to the HOer that he needs to spend a couple $K for another mechanical unit, or to the business owner why we need to eat the $$ probably isn't his favorite choice.

Perhaps, this place will eventually dry out, and this thread will be moot. 

Great input everyone!


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