Brian,
Your missing the connections because you’re not looking at the entire picture.
It sounds like you have a background in HVAC?
Just enough to get you in trouble.
[FONT=Arial]I have worked in HVAC, Indoor Air Quality and air balancing, ran an energy retrofit , air sealing and energy audit company, taught building science in the arch faculty at a large local university, wrote the energy regulations for the province I live in, have an almost $50K energy retrofit QC and supervision contract from this province at present, and have been in the energy field in some respect since 1977. In the 1989-1993 period, two of my builder clients (who I was advisor to) in our national “R2000” high efficiency home program were named Canada’s “R2000 Builder of the Year”. So yes, I have a bit of experience in these subjects.
What does insulation do? Well, it depends on its type. Installation of itself reduces conductivity. Often applied with a barrier, insulation will reduce vapor, moisture (liquid) and air infiltration.
If we are missing insulation, were likely missing any form of vapor retardant.
Water vapor travels from high concentrations to lower concentrations. Without an adequate vapor barrier moisture will travel through the ceiling materials increasing water vapor content of the air within the house.
Vapour diffusion is only responsible for less than 2% of moisture movement in most conventional houses so there’s going to be very little coming down through the uninsulated ceilings. There’s a Q&A section answer in the recent issue of Fine Homebuilding in which the consultant says that vapour retarders are not needed in homes…How’s that for a change in theory??? It’s been said many times in the past 30 years. Check some of my posts in other threads. Joe Lstiburek (Building Science Corp), a leader in the Building America program, recommends a top notch basement insulation system with an air barrier but no vapour barrier installed.
For starters, heat does not radiate into the room through the ceiling. It’s form of heat transfer is conduction.
It may radiate into the room through a window. So, your implication that the radiation will not cause condensation is an accurate assumption. However, I don’t think this is what you meant.
David:
Your website says you took a building science course. Ask for your money back!
Heat certainly does radiate down from ceilings if they are hotter than the objects/surfaces below them. In the Texas area, I would imagine attic temps would have to get to the 130-150 deg F range in the hottest weather (unless leakage of cooled air from bad duct systems is cooling the attic also). SO if the attics temps are say 130, the drywall with no insulation over it can be 100-110 or so and will radiate heat to the 68-70 deg surfaces below. The 110-120 temps are the operating range of some electric and water radiant ceiling heating systems installed above drywall. So if the heat does not radiate down, how can the vendors stay in business? On another item…In the south, foil reflective radiant barriers are installed under the rafters to prevent the heat radiating from the bottom of the roof sheathing from heating up the attics and eventually the ceilings which then radiate heat to the room. Yes, the heat does conduct down through the wood sheathing and drywall, but once it gets to the lower surface, much/most of it is “emitted” as energy in the infrared electromagnetic radiation range (if the air is relatively still).
Cold air lowers the temperature of the supply air grill. Correct, hence condensation on the cooled grille after the air handler shuts down but not while running as it should be supplying dehumidified air. The supply air grill is a penetration through the ceiling. The lack of insulation, (thus lack of vapor and air infiltration retardant) results in increased air infiltration around the register which then reduces heat energy from the air entering and condenses water vapor on the supply register.
In a warm/hot house and especially hot attic, the buoyant ,lighter air will rise, and should not be coming down around registers (how big are the gaps you’re talking about?..pretty bad installations then). After all, this is the theory of attic venting- hotter air leaves the upper vents, drawing cooler (although sometimes 100+ deg air) in the lower vents. The immediate air pressure regimes around these grilles should be at a slight positive pressure relative to the attic (a good micromanometer will show this), so air should not be falling or moving from the attic downward.
That is correct, if this is in fact the case. We must first show that the increase of water vapor (latent heat) and sensible heat (conduction + radiation turning to sensible heat when it hits a surface) is not exceeding the HVAC units capacity in btu/hr. If we conducted a psychrometric evaluation and provided this information to you, maybe you could figure that out. However, this is only an assumption. We don’t know if the air-conditioner is in fact running longer and keeping up with the heat load, however thermostat is on a 80° wall, so it probably won’t shut off. It all depends what somebody set it at .
We must consider the geographical location where Mr. McKenna conducts his business. It is very hot and it is very humid.
Correct.
Missing insulation does not radiate moisture or temperature (do you mean “heat”). But it does conduct (and allow an increase in radiation), and as we said heat radiation does not increase humidity.
However, moisture is passing through the wall/ceiling where the building envelope construction is inadequate. It is likely (more than likely) that the association of decreased insulation is equivalent to decrease vapor retardant materials. (True but possibly an insignificant amount)
It is removing more moisture. However, reducing the moisture level in grains per pound will increase the transmittance (no, diffusion) of water vapor through the building materials. What makes you think that the air-conditioner can keep up with this infiltration (infiltration is air movement not diffusion)? We are missing too much information here to be making these assumptions. Through psychrometric evaluation we can determine the sensible heat factor, however none of these evaluations were performed. Without additional information (which is outside the scope of Home Inspection), I think that the association between moisture condensation and building envelope deficiencies is a fairly accurate assumption on the part of Mr. McKenna.
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