AboutBruce E. Johnson Expertise I can answer any construction related question in regards to carpentry, concrete, drywall, masonry, structural elements of any type of building, residential or commercial. Interior or exterior.
Experience Custom Commercial and residential buildings. Churches, theaters, schools and auditoriums. Most recently I am working with the Catholic Church on several design build committees. I have a website related to scheduling and project supervision. Although my expertise is more related to multimillion dollar commercial, educational and theatrical projects my generous credentials in residential and remodelling construction make me a viable source of information regarding all forms of building questions.
Hi. My mom lives just west of Minneapolis, MN and owns a 3-bedroom ranch-style house with a finished basement and an unfinished attic. It was built in 1963 and rebuilt in 1965 after being hit by a tornado <bummer, that>. It has 2x4 outer wall framing with fiberglass insulation filling the cavities, Build Rite sheathing or similar with solid cedar siding over that. There is no vapor barrier in the walls (in 1963? They'd have said, "Vapor barrier? We don't need stinking no vapor barrier!") and drywall on the interior wall faces. There is (no kidding) 3 and 1/2" of blown cellulose attic insulation (even with the bottom of the roof trusses). The roof was re-roofed about 5 years ago with ice and water shield and light-gray asphalt shingles. The gutters are in good repair and drain water at least 15' away from the foundation. There is a natural gas furnace driving baseboard water radiators, no central air, and a gas-fired water heater. Mom uses a dehumidifer in the basement in the summer and a humidifier upstairs in the winter. There is a gas-clothes dryer, a range hood, and 3 bathroom fans.
I had the gas company and the electric company each send an energy auditor out last summer. Some high points of their respective audits were:
1) The house is a leaky as a sieve, about 3x more than a comparable new house.
2) One exception to this "breathable house" was in the furnace room, where a particles were found on the top of the water heater - evidence, said they, of a weak draft or even back-drafting. Both recommended adding a combustion air source - a 6" flexible duct through the outside wall with a 2-3' cold-air trap at the bottom. An explicit combustion air source is now Minnesota state law.
3) Both recommended adding attic insulation after sealing off the attic bypasses.
4) Both recommended damp-proofing the crawl space (underlies the east third of the house)with cross-linked poly and a special 3M plastic tape for the seams. The plan would be to lay the plastic down on the ground and run it up the foundation walls, sealing it off w/ construction adhesive to the ?mud sill? (the plate on the top of the foundation concrete block wall). The idea is create a moisture barrier over the ground and foundation walls, then make the crawlspace airtight by sealing cracks and the crawlspace vents, and then insulating this space.
By the way, I (the devoted son) am 40, and have worked as a glazier and window installer, maintenance guy (which got me experienced in repairing & renovating 1920's era construction), and have 3/4 of a degree in mechanical engineering.
Since the audits, I have done quite a bit of reading about building science. I have come to the understanding that well-intentioned changes of even a single aspect of the heating/ventilation/appliances/insulation/moisture control/etc. house equation can potentially cause great and expensive problems, and so one must consider all the impacts of a course of action, considering the house as a total system. I have some concerns.
I think this house has worked well in many respects (free of mold, good ventilation, healthy house), but at the expense of fairly high heating costs (the 3 wall-mounted air conditioner units are used about 15 days a year or less).
My plans include:
1) Make the ceiling/attic interface as airtight as I reasonably can from the top using expanding foam & silicone silicone sealants, drywall, etc., then adding about a foot and a half of blown cellulose after adding ventilation chutes over the roof/outer wall intersections.
2) a) Moisture-proof the crawlspace as previously described. b) Caulk/foam seal the wood joints over the foundation walls where air might come in. c) Seal off the ventilation holes. d) Insulate with fiberglass batts.
3) Add a combustion air source, 4" or 6" with a 3' cold-air trap in the furnace/water heater room. (I.e., make a hole in the wall, then run insulated flexible duct down to the floor and up vertically 3'.)
I have two questions.
Question 1: For insulating the crawlspace, one auditor recommended draping fiberglass insulation directly over the (sealed) foundation walls. A home-improvement book I read said in my climate, the only place to insulate was directly under the floor, by suspending kraft-faced fiberglass batts between the floor joists.
Which is right?
2) I'm concerned about fresh air ventilation & moisture accumulating in the walls after I make these weatherization improvements. In the winter up to now, the house has run a somewhat negative pressure (due primarily to sustained furnace use creating a partial vacuum in the house). At the cost of fuel, two other very important benefits were realized: the overall airflow through the non-vapor-proofed walls was from the outside-to-the-inside, drawing cold & (most importantly) dry air in. The happy result was plenty of fresh, healthy air and dry, mold-free wall cavities. Once I tighten things up and add the combustion air source, the net "suck" or negative pressure in the house will be reduced (which will strengthen the draft of the furnace and water heater, which is good), but the walls will have less tendency to stay dry.
How do I make sure the walls stay dry inside and (secondarily) assure adequate fresh air for a healthy home?
Thanks for your help and insight!
Curt
Answer Hi Curt, sounds like you have looked at the situation from all angles. As to your question regarding insulation for the floor system: I recommend the batts between the floor joists, this allows you to ventilate the crawl space without sacrificing heat loss through the floorboards. As to your second question: by adding the outside air to the furnace you are in essence still getting the air as before except this time it is being treated by the furnace prior to entering the house as opposed to entering the house and then being drawn into the furnace for treatment. The improvements you are doing will only enhance the efficiancy of your heating and cooling thus keeping the house even better capable of dissipating moisture. Not to worry, you are on the right track. Go for it...I hope this information helps feel free to write again regarding this or other matters, sincerely bruce e johnson
