For those with moisture meters...questions...OT?

Re: For those with moisture meters...questions...OT?

That blackening and mold reflects that the attic space is not properly ventilated. 

Air infiltration will certainly increase his energy bills.  I heat my2,000 sqft home in NW PA with a ground source heat pump.  Since I purchased my home, I have replaced all the windows (22 of them) with insulated double pane pvc windows that do not leak air.  I have added an additional 6"of insulation to the attic space (12 total).  I also removed and replaced the plywood with perforated soffits the full length of the over hangs on both sides of the house and installed a ridge vent.  I added insulation in the joist spaces above the basement walls.  I have searched for drafty outlets when the wind is blowing and have carefully sprayed spray foam around the outside of the outlet box.  When we resided the house I had an aluminized mylar foam house wrap applied that lets the house breathe, but stops air infiltration. I have replaced our outside doors with insulated doors with good weather seals.  Our house still has some small drafts when the wind is really strong, but nothing like it used to be.

We pay about $1200 per year for our total electric home for our power.  We do not have wood heat nor other source of heating or cooling.  We do run A/C in the summer months.  I have a Carrier Infinity geothermal heat pump that is about 1-1/2 years old.  My house has been heated with a ground source heat pump for over 40 years.

I'm confused

1% higher than the surrounding unstained area. ......it doesn't take much change to result in a piddly 1% difference.  Given the insignificance of this difference why is it important?

I am nearly certain the darkened areas are from a "micro climate" situation caused by the fact it is on the cold side of the house...... If it is mold you surely know that mold only develops on wet wood.  Wet wood under sound roofing is not a result of any micro climate.  The question be be asking is why has the sheeting been wet?  Ice dam in the past?  Shingle leak?  Is the source of the leak still present?

If So my question is, does the darkening of the wood change it chemically enough that the meter notices it?     It certainly could.  If dark, the mold has deposited stuff and consumed cellulose.  But I remain confused as to why this question has any importance. 

Re: I'm confused

My guess that the inside of the sheeting is usually covered with ice from poor attic ventilation and the mold starts when the attic warms and stays wet longer than anywhere else up there. My neighbor across the street has a house on a slab. At certain times of the winter the sheeting is covered with ice. Crazy looking when even the shingle nails poking through have ice on them too.

Re: I'm confused

As a Home Inspector for over thirty years I have seen scores of attics with the underside of the sheeting darkened by mold with out evidence of a roof leak.  Also many that were damaged by roof leaks. Under the right set of conditions moisture will condense and soak into the sheeting leaving it wet enough for the mold to darken it.  The "micro climate" comment was to point out that this was occurring on the northern side of the house but not the southern side.  There are many variables...Orientation, type and amount of ventilation, amount of attic insulation, type of heat and AC, etc. Can't tell you how many attics I saw with a perfect rectangle of darkened sheeting above the bathroom.  It falls into the category of "Things that happen must be possible".

There are some critical levels of wetness.  At or above fiber saturation the sheeting can rot, below that you may get more harmless superficial mold often called mildew.  Depending on species fiber saturation is around 20 to 22%.

Temperature is also critical.  Too cold and condensation will occur and maybe even frost but if it's too cold the mold will not grow.  At some point it has to be wet enough to burst the spores to get them growing.  Once the spores burst it takes far less moisture to sustain them.  It has to stay in the "Goldilocks' Zone" for about ten days or two weeks for growth to occur.  So some of these spots reach the right conditions in the fall and again in the spring.  Tremendously more complicated than anyone would think.

So, for whatever reason some of the wood sheeting is darkened and I was wondering why it meters differently that unaffected wood.

Re: I'm confused

I had a customer once whose teanage daughter would take hot showers long enough to use all of the hot water. There would be icicles hanging in his attic. I think the only fix for that was to vent the bathroom on through the roof.

Otherwise, I’m sold on the aluminum faced decking, but not for this situation. It eliminates the radiant heat coming through the roof from when the Sun is heating the other side.

Physics, Not Chemistry

Moisture meters work on the actual amount of water in the wood.  Pin types measure resistance to the slight charge flowing between the pins.  Pinless meter measure potential conductivity.

If your sheeting's lignin has been degraded, like a sponge, I'll bet it's more prone to absorb more water vapor at any given time than the surrounding (unaffected) wood resulting in the readings you're getting.

Have you taken a reading on the rafters in the different "micro" areas?

Re: I'm confused

Thanks Keith.  I was wondering if were physics or chemistry.  I have seen the icicles hanging from the roofing nails and frost on the underside of the sheeting.  I recently put the foil baked sheeting on one of my rentals. I spotted a bundle of it hiding on the top rake in Lowes and watched it for a long time.  When I needed a new roof and some new sheeting I talked the manager into selling it to me at a discount.  The tenants are idiots and will not be able to tell the difference.

Re: Physics, Not Chemistry

I thought about the physics Vs chemistry part and couldn't sort it out in my mind, but don't really care what you call it.  I am trying to decide if the degraded wood meters differently of if the process that degraded the wood is still in effect.

My son wants to install spray foam and I am stumbling through figuring out the drawbacks of adding it to a house not built for it.

This house has been amazing. Built in 1994 and clearly been remodeled and modified.  We think the second HVAC system was added when they started finishing the basement.  So now one system does the top floor and the other does the middle/main floor and the basement except we find a duct or two that are still active on the top floor from the basement system.  One bedroom has one from each system.  There is an abandoned duct that may have been for the hood fan but makes no sense. Gas and plumbing runs from one end to the other of the house that could have been fifty feet shorter.  A single woman with lots of money lived there and I think contractors just took advantage of her.

Just trying to help my son cut his electric bills.

Foam

In my area (North Jersey)  the skinny is, if you find foam (Great-Stuff or similar) in a potential buy, either plan on the cost to remove it or move on.  Does a great job of blocking air infusion, but also keeps the termites warm and undiscovered.

You know, Barry.  A house has to breathe.

variables affecting reading

First,  a 1% difference is tiny.  The very best commercial dry kiln meters only claim repeatability of 0.5%, or more at higher levels of water.  Measurement is affected by more than simply amount of water.  For the most accurate readings with a commercial pin meter temperature and wood species must be corrected for.  (I have no experience with surface contact meters).  If mold grew the mold ate wood, deposited mold poop and left a layer of mold bodies in some state of aliveness.  Either factor could cause this tiny difference.  Or, the degraded wood or poop or mold could reach a different equilibrium moisture content.

I am not denying the observation but it seems an attic would have to be poorly ventilated to reach the dew point in one part of the attic.  Sun on one side of the roof should set up robust convection from eave vents to ridge vent which will blend any micro climate in the attic.  I don't see any significant moisture transport through well installed felt and shingles. 

Re: Physics, Not Chemistry

if the process that degraded the wood is still in effect..................By "process" do you mean mold growing or the process that may come and go that enables mold to grow? A moisture reading will tell you if the wood is wet enough to grow mold.  However, if the problem is that some part of the attic reaches the dew point some times in the year you won't figure that out with a meter.  Fix the attic insulation and ventilation.  A quality home inspection would have warded off this issue    . 

Re: I'm confused

By any chance do the bathroom vents discharge to the attic space? If so they should be plumbed to the outside and not under ventilated eaves as the warm moist air can go up into the attic through the soffit vents.

The north side of any roof is going to be cooler so any moisture in the attic air is more likely to condense there.

Re: I'm confused

Back to my suggestion of bathroom vent relationship. Was there a bathroom under that portion of the roof? If so, I would bet that is the source for the moisture, so I would see about sending a double wall or insulated flu out the roof, or gable if it’s close enough. 

If your son wants to spray bleach on the inside roof deck, make sure he wears a canister air filter, or fresh air supply from outside. Breathing that stuff will wreck his lungs otherwise. 

And about the foil faced decking. Back about 16 years ago I added a new master bedroom onto my nephew’s home. It had a cathedral ceiling, so I used the little styrofoam vent channels to allow air to travel from eve to ridge vent. But before that went in, I spent several summer days up on scaffolding constructing a large semi-elliptical window on the gable. During that time I never felt any heat which would have been slowly roasting my brain without it. 

Re: Physics, Not Chemistry

Unfortunately my son and his fiancé bought this house at the peak of the market, a seller's market no home inspection allowed.  He was given an hour to look at the house.  I walked through it with him and pointed out a number of issues including the attic ventilation issues.  I also pointed out it is at the bottom of the hill with a steep driveway.  Unfortunately they would have bought the house regardless of anything I said.  (Sometimes they can't tell when they really should listen to Dad.)

Re: Foam

Very Interesting, I had not heard of the termite aspect.  I will check and see if that is an issue here.  Would not be surprised, with all the rivers around this area is the termite capital of the state.  

It's amazing to me what we don't know about building houses.   Remember Dryvit the exterior foam and fake stucco siding?  A long running disaster.

I am somewhat skeptical of filling wall and roof cavities with foam.

I am also baffled by the idea of sealing houses so thoroughly that you have to install an air to air heat exchanger for ventilation.

Re: variables affecting reading

That's kind of my thinking.  The darkened area has been modified in some fashion by the mold.  Whatever it is may be causing the meters to react differently.

It might be a good idea to spray this area with something like BoraCare to be sure the stain is dead.  One of my objections to the spray foam is that it conceals the sheeting and may be concealing whatever the process it.  Some future roofer may step through.