Repainting a house that lacks vapor retarder

Q.   In an earlier post, you commented on a house with wood siding that paint would not adhere to, peeling off within two years, probably because it lacked a proper vapor barrier on the warm side of the walls. This is an issue we are aware of in our home. We are about to repaint our home and I wondered if you could offer any suggestions as to how we may best deal with this.

In my search for useful suggestions on this subject (my thought process hoping for some sort of advanced product to use in our painting) I ran across a product “permanent coatings,” but they were in Vancouver. I didn’t know if that could be an answer or if it is even sold in the states. Nevertheless it made me even more curious as to whether or not there may indeed be a technologically advanced product out there that could bring us salvation!

A.  I do not know anything about the product you mention, but I am very wary of the hoopla about some products that claim miracle solutions. Moreover, this coating is for exterior application in lieu of regular paint. It does not solve the convection and diffusion of moisture into the exterior wall cavities, which are the cause of the problem.

A vapor barrier is needed on the warm side of the exterior wall to prevent moisture from migrating into the wall cavities and causing major paint peeling, and potentially worse problems.

The most important thing to do, to provide an effective barrier to moisture convection into the wall cavities, is to check for cracks and minor openings on walls and ceilings; where different materials meet, such as window and door trim and baseboard; around electrical ceiling fixtures, switch and receptacle boxes. These openings, however minor, should be caulked.

Hardware stores sell closed-cell gaskets that are installed under the cover of switches and receptacles.
The walls can be painted with B-I-N, followed by your choice of finish paint or two coats of a low-perm paint.

Insulating bedroom floor over unheated garage

Q.    My bedroom is located over an unheated garage. The unfinished garage ceiling is insulated with two layers of rolled bat insulation. The paper vapor barrier is facing the garage, not the bedroom floor.

I would like to seal off the garage ceiling with foam boards to stop any cold air from coming in through the bedroom floor and to provide some additional insulation. My understanding is that the vapor barrier should be next to, or on the side of, the heated room. Does this hold true for my bedroom/garage situation? Must I reinstall the insulation with the vapor barrier next to the bedroom floor before I put up the foam board?

A.    Ideally, yes but we know that paper vapor retarders are not very effective. Moreover, the addition of at least 1-inch thick rigid insulation will warm the joist cavities and reduce the chance of condensation within them. It will also reduce any heat loss through the floor joists.

And if your sub-floor is plywood, that in itself is an effective vapor retarder. However, pull down some of the fiberglass insulation in a few widely scattered spots, particularly next to the outside walls, and check for any signs of moisture or mold development. If you find any of these, you should seriously consider pulling the insulation down wherever these conditions are visible, allow the areas to dry and put the insulation back (if it is dry) with the paper vapor retarder facing the bedroom floor.

Be sure that the entire joist cavities are filled with fiberglass insulation to prevent heat loss and cold air from infiltrating between the top of the insulation and the subfloor. You are unlikely to find that the entire area has been affected.

Also be sure that you use extruded polystyrene rigid insulation (XPS — blue, pink, grey or green). Remember that rigid insulation on the garage ceiling will have to be covered with fire-code drywall, properly taped.

Ventilation needed for healthful indoor air

Q.    In a recent article about installation of a housewrap in combination with Styrofoam, you said that houses should breathe through ventilation. What do you mean by that?

A.    Many houses built since the energy crisis of the early 1970s (especially in the last couple decades) are built to be very tight to conserve energy. This is a noble goal but it has resulted in some unhealthy indoor air. Dust, mites, outgassing of manufacturing processes in furniture, building materials, carpeting, etc. contribute to this unhealthy atmosphere. The result may be allergic reactions in sensitive people, increased relative humidity, mold build-up, etc.

A well-ventilated attic is helpful in dissipating moisture that migrates from the living space but it may also be necessary to ventilate the conditioned space as well. This can be done in a low-tech fashion by the judicious opening of windows, or by the use of fans exhausting to the outside as long as there is an adequate supply of make-up air. (Otherwise, the heating system may back-draft — a serious and potentially lethal issue.) Or a whole-house air-to-air heat exchanger can be installed.

Improving insulation in walls while re-siding

Q.    I want to increase the insulating value of our siding on our Cape Cod home. Another feature would be to gain extra sound proofing. Right now, we have regular vinyl siding — but not all continuous lengths.

I am thinking of removing the present siding then covering the house with some of that “pink” material to get added insulating value. Then cover with a heavier vinyl siding with foam backing. In addition to the above, should I add a vapor barrier? Any other suggestions, for example, caulking?

A.    What you plan on doing will definitely accomplish your goals — 1-inch extruded polystyrene (blue or pink) is the best thickness to use, combining efficiency and practicality for the siding installation.

However, you do not want to install a vapor retarder on the cold side of an exterior wall in climates where the heating season is greater than the air-conditioning season (in the deep south, vapor retarders should be installed on the outside – the warmer side – of exterior walls.)
No caulking is necessary; properly installed vinyl siding trim pieces will take care of draining water.

Insulating walls of a 1950s ranch

Q.    We have a 1951 vintage ranch in northern NJ. The house now has good modern Andersen windows. But I’ve found that the original exterior walls literally are hollow — no insulation of any kind whatsoever. Adding insulation to these empty walls is my latest project.

The wall construction from the inside out is: Sheetrock, air gap (2-inch by 4-inch stud space), chipboard with black tar-like surface, wooden clapboards, plus 1987 foam board, approx 3/4″ thick with a silver surface facing outside and vinyl siding.

Because of the finished exterior vinyl siding, I’m inclined to add  insulation by boring through the Sheetrock with a hole saw, blowing  in cellulose insulation, then patching, spackling and painting. I  know it will be messy this way. Fortunately, I only have 3 rooms to do.

However, in mentioning this plan outline to a coworker, he was concerned about my lack of a vapor barrier. He was of the opinion that the cellulose could become a humidity sponge that would then create an ideal environment to foster the development of mold. Your thoughts?

Also, any suggested alternatives to blow-in cellulose, such as spray-in expanding foam, would be appreciated.

A.    First — a slight digression — although “Sheetrock” is used generically, it is the trade mark of USG and should be capitalized. (I have made that change in your question.)

You will be taking a slight risk blowing in cellulose as you now have a vapor retarder in the aluminum foil of the rigid insulation added in 1987 — on the wrong side of the walls.

You can retrofit a vapor retarder on the inside walls, but you’ll never be sure that it is foolproof. This can be done by painting the inside of the exterior walls with B-I-N topped with a finish paint of the color of your choice, but there will be interruptions in the coverage at the intersection of the interior wall with these outside walls, and where there is trim, electrical boxes, etc.

A safer alternative is to have closed-cell polyurethane sprayed in the stud cavities. It is an expensive process, but it will reduce your energy bills substantially while increasing your comfort. You should recover the capital cost over the years if you stay in the house long enough. Or,  if you move, the house should be easier to sell.

One word of caution: Insist on closed-cell polyurethane. Do not accept open-cell polyurethane such as Icynene; it absorbs moisture and should never be used if there is a vapor retarder on the cold side of the walls in moderate to cold climates.

Paint keeps peeling from wood-shingle siding

Q.   We have a chronic problem with peeling paint on our 50-year-old wood-shingle home. After complete sanding, priming and painting (Benjamin Moore house paint), paint will begin to peel in two years on all exposures — full sun or heavy shade though most of house is shaded by mature trees. The exception is an addition, which does not peel. We are in the process of repainting again! Can you advise any primer, paint or technique that will eliminate the problem?

An alternative is to have the house clad in vinyl siding. However, I’ve been of the opinion that siding detracts from the home’s value. Do you agree?

A.   From your description, I think you have a problem with interior moisture pushing the paint off the shingles. Although most paint failures are caused by improper preparation and/or application of the coatings, as well as from external factors such as exposure to the elements, the fact that yours fails on all sides of the old part of the house but not on the addition makes me suspect that there is another reason. Your 50-year-old house may not have a vapor retarder on the warm side of the exterior walls and it may also have had insulation blown in if the house was not insulated at the time of construction (too often the case with that vintage house).

In the absence of a vapor retarder, warm, moisture-laden air works its way mostly through any cracks in the walls’ interior finish and other avenues, such as electrical boxes, and also possibly through it depending on how permeable it is. As it cools, condensation occurs on the back of the sheathing. This condensation works through the sheathing into the shingles and pushes the paint off.

And if insulation was blown into the walls without the addition of a vapor retarder on the warm side of the exterior walls, the insulation can get wet and the same process happens. But this is more serious as wet insulation not only loses some of its R-value but structural damage can occur in time.

If you know or can find out whether or not there is a vapor retarder, and if insulation was blown in, write again and we’ll take it from there.

If I am right about your moisture problem, covering it up with vinyl siding would only hide the problem.

Water drips from cathedral ceilings after cold spells

Q.    I am a self-employed building contractor and have followed your column for years. The problem that I am having is with two separate additions that I built within the last two years.

Both additions have cathedral ceilings with skylights. The construction consists of 2-inch by 12-inch rafters, 24 inches on center, with 5/8-inch tongue and groove plywood decking. The roofing material is 30-year asphalt shingles applied over No.15 felt paper, with Grace Ice & Water Shield applied around the perimeter of the skylights as well as to the bottom three feet of the roof. There are continuous 2-inch soffit vents as well as a continuous ridge vent on both additions. The rafter bays have plastic baffles for ventilation from top to bottom. R-38 faced-fiberglass insulation was applied below the plastic baffles and was stapled to the rafters. The ceiling is made of 1-inch by 6-inch tongue and groove beadboard applied to the bottom of the rafters.

The problem is that every time we have a real cold snap followed by a quick warming up period, I get dripping from the cathedral ceilings occurring on the inside of the additions. My first thought was that maybe the ridge vents weren’t performing correctly, so I tore off the existing vents and did them over. I noticed a considerable amount of condensation on the bottom side of the plywood as far down as I could see.

I contacted several architects I know as well as other people in the trade. The consensus was that because of the cold, condensation built up, and when the weather warmed the frost on the bottom side of the plywood melted, thus creating the dripping which took place. Hopefully you can provide me with some help in resolving this situation.

A.    I have bad news for you. The people you contacted are correct in saying that considerable condensation occurred during the cold spells. The subsequent dripping comes from the fact that the condensation froze on the underside of the plywood roof sheathing and melted when the temperature warmed up.

But the condensation takes place because you used faced-insulation and tongue and groove boards on the ceilings of both additions but did not provide an air barrier. Moist, warm air convects through the joints between the ceiling boards and bypasses the kraft paper vapor retarder. When it comes in contact with the cold roof sheathing, condensation occurs. No amount of ventilation can overcome this scenario.

If you had used unfaced fiberglass insulation and carefully stapled on 6 mil plastic as a vapor retarder, and had no ceiling perforations such as electric boxes, etc., you would not have this problem.

Unfortunately, there are only three ways to remedy this situation. One is to remove the ceiling boards and carefully staple 6 mil plastic to the underside of the rafters. The second is to remove the roof and the insulation and to spray closed-cell polyurethane between the rafters. The third and most appealing option is to have an experienced foam insulator remove the fiberglass from the rafter bays with hooks they insert from the fascia and the ridge vent and inject closed-cell polyurethane.

Adding attic insulation

Q.    I have faced insulation that I want to install over existing insulation in my attic. Should the insulation be placed with the facing up or down? Thank you for any information.

A.    The vapor retarder should be peeled off before you put the new insulation over the existing one. A vapor retarder should not be on the cold side of the insulation and should not be sandwiched between two layers of insulation unless the R-factor above (on the cold side of) the vapor retarder is twice as much as the R-factor below (on the warm side) of the insulation.