Building a room underneath a deck

Q.    My 17 foot by 22 foot deck is high enough off the ground to accommodate a room underneath. It is not quite high enough, however, to provide enough space for a person to work in the space between the roof of the proposed new room and the rafters of the deck. My question is whether you are aware of any construction technique or material that would allow me to create a waterproof ceiling for the room beneath the deck without either 1) taking the deck apart or 2) making the deck surface itself the roof. That is, is it possible to seal the new roof from the bottom side?

A.    What I will describe to you is not a standard construction technique, but I have used it myself for the same purpose. The issues to address, and steps  to take, are as follows.

  • You will have to support the deck in order to remove the beam and the posts.
  • You didn’t mention whether or not there is already a concrete patio under the deck. If there is, does it have frost walls around its perimeter? If there are no frost walls, the slab may not be strong enough to support the new construction. This needs to be addressed.
  • The most crucial part of this system is how to waterproof the joint between the house wall and the new roof. Even if you have a very wide overhang, you will need to be extra careful that rain splashing on the deck or under windy conditions is not allowed to creep behind any flashing that you use. It is best to make a saw cut into any vertical wood siding or insert the upper leg of the flashing under horizontal wood or vinyl siding. The lower leg of the flashing should extend a minimum of 16 inches under the deck.
  • Screw a pressure-treated 2-inch by 6-inch to the deck joists at the mid point and another one where the beam used to be, and where the new walls will be built.
  • Either find U-shaped aluminum channel stock with 3-inch legs in a metal fabricating shop, and have them cut enough of them in 5-inch lengths to be installed 16-inches on center under the outside board, or have them make them up for you. Screw them upside down with the opening facing the house.
  • Choose metal panels with “v”s; avoid corrugated panels.
  • From underneath, screw the selected metal decking material to the flashing at the house wall, using 1-inch aluminum or plastic tubing as spacers.
    Screw the metal decking to the middle board, using 2-inch tubing as spacers. Let the metal decking run under the aluminum channels to where the room ends (you can also have the metal panels run past the walls of the new room to provide an overhang).
  • Caulk the double-V overlaps of the metal panels generously with polyurethane caulking compound, and screw each panel to the next.
  • Screw a 2-inch by 2-inch piece to the house wall to give additional support to the roofing material.
  • Stick W.R. Grace Ice & Water Shield (or equivalent) under the metal panels, starting at the top and overlapping each sheet by a couple of inches. This is to provide additional protection in case water works its way around the caulked metal panels overlap.
  • Next, build the outside wall firmly in contact with the metal decking to support the deck. Remove the temporary supports.
    Build a framework for the roof made of 2-inch by 4-inch lumber (there will be no live load such as snow or people walking on the metal panels since the deck will protect the roof below). Keep the roof framework 2 inches below the metal panels, as the safest way to insulate the roof is with closed-cell polyurethane that should fill the space above and between the roof framing, giving you approximately an R-44 roof.

I would strongly discourage you from using fiberglass in the roof – it’s a recipe for problems down the line. The room’s walls can be insulated with fiberglass or foam.

Special tool will open valves for toilets and sinks

Q.    I recently moved into a new-to-me house. I just discovered a slight leak in a joint of the feed pipe to one of the toilets. I tried to shut the water off at the little oval valve that supplies water to the toilet tank but it is frozen so tightly that I could not budge it and I am afraid I will break it if I use a pair of pliers. I remember your mentioning some time ago that there is a special wrench for these valves but I didn’t save the information as I didn’t need it at the time. Could you please respond quickly as I do want to change the feed tube as soon as possible.

A.    Glad to oblige. The wrench you are referring to is the Gordon Wrench, a plastic tool that fits tightly around these fragile valves for toilets, kitchen sinks and vanity lavatories.

Gordon Wrench
Gordon Wrench

These valves become frozen over time and, when you need to operate them to replace a washer, stop a leak or perform some other repair,  refuse to budge and often break, leaving you stranded. This ingenious wrench allows you to apply some leverage to these contrary valves without the risk of breaking the fragile handle; I would not be without one.

If you cannot find it in a hardware store, discount store or home improvement center near you, you can order it via the Web at

Small leak and ice dams persist after re-roofing

Q.    We had a new roof put on about two years ago. The old roof was taken down to the bare wood. We had 6 feet of a water shield (whatever the name of that is) put on the eaves. We had a new gutter put on with leaf shield (the wire kind). We had a new bow window put on at the same time.

We get long icicles when there is a lot of snow on the roof. I thought the water shield would stop any leaks into the house when there is an ice jam in the gutters. We still get a comparatively small leak coming into the house. We have been thinking of putting an electric wire snow melter in the gutter, but we have heard that is not the best solution. We have read that insulation, either blown into the eaves, or a thick layer of insulation put into the eaves might help.

The house is a one-story house. The gutter is L-shaped. I wish I could describe it a little better, and I assume you would have some suggestions as to how to prevent the leaks when there is an ice jam. Can you help? ( I am a little too old to do very much by myself.)

A.    The waterproofing membrane you had installed under the new shingles should prevent any leakage from water pooling behind any ice dams. However, if a proper flashing was not installed behind the gutter, it sounds to me as if water gets into the soffits of your house between the fascia board and the roof sheathing as the gutter fills with ice. This would account for the small leak.

What should have been done before installing the gutter was to install a bent flashing with its upper leg under the waterproofing membrane and its lower leg over the fascia board before installing the gutter. This way, the open joint between the roof sheathing and the fascia board would have been securely sealed. Correcting the problem will require removing the gutter and pulling up a few inches of the bottom of the membrane to slip the flashing under it. If the membrane cannot be pulled up enough the flashing can be installed on top of it but a new strip of membrane or compatible tape will have to be put over it and the existing membrane to prevent water from getting under the flashing.

I agree that putting an electric heating cable in the gutter is not the best solution; it will not stop the gutter from freezing. To reduce or prevent the incidence of ice dams is another story, however. Do not have any insulation placed or blown into the eaves; it can get wet and it will never dry. Moreover, there is no need for insulation in a cold space; insulation is only helpful to slow down the heat loss between a heated space and a cold one.

Adding insulation in the attic is very helpful but can be difficult to do if the attic is floored and is used for storage. Effective ventilation is also helpful and is best accomplished with a combination of continuous soffit vents and an externally baffled ridge vent as long as there is an uninterrupted airflow between them.

Removing moss from retaining wall

Q.    Moss is growing on a cement block retaining wall. I would like to remove it and also prevent recurring growth. I have applied laundry bleach full strength that temporarily killed the moss but after another period of hot, humid weather, it grows back. Is there a method for removing it permanently?

A.    Removing the moss growth with bleach is a very good way to go but to keep it under control for at least one year, spray it with Moss & Mildew Killer. If you cannot find Moss & Mildew Killer locally in a garden supply, hardware or large discount stores, you can order it online at Moss & Mildew Killer comes in 2-pound shaker boxes or as hose-end sprayer.

The manufacturer claims that it will not damage shrubs, trees or lawn, but you should read and follow the directions carefully and follow them. It is said to be effective for a year.

Replacing backfill next to concrete-block foundation

Q.    I have a problem with the basement wall on the higher-grade side of my house. The wall is built of 11 courses of cement blocks and was backfilled with the native red clay and other soil when the house was built 48 years ago. I suspect I was in a hurry when I built the house so now I have to redo the backfill. The basement wall has not moved much but the hairline crack in the mortar joint indicates that the wall is moving.

I need to know the proper fill material to use and the proper way to grade the soil to prevent a future problem. The wall is 36 feet long and the house is a one-story brick ranch. I don’t see any cracks in the mortar joints of the bricks yet. I would appreciate your views on this situation.

A.    If you only see a hairline crack in a 48-year-old concrete block foundation, I wonder why you would want to go to the trouble and expense of excavating the affected wall and redoing the backfill. Keep in mind that there are some risks involved in removing the existing soil next to the foundation; it will take an operator who is very experienced with the use of a backhoe, as well as some hand shoveling. At this point, I would suggest that you simply make sure that the grade slopes away from the wall in question at the rate of about 2 inches per horizontal foot and plant a healthy stand of grass on it to control the travel of water.

However, if you want to replace the existing backfill, have the soil excavated to the base of the footings. On the side of the excavation away from the house, pin a sheet of geotextile fabric wide enough to start at the bottom of the trench and eventually cover the stone bed you will install. Spread a couple of inches of egg-sized crushed stones at the bottom of the excavation.

Lay a 4-inch perforated drainpipe on top of the stone bed and, at the lowest point in the grade around your house, connect it to a solid drainpipe leading to daylight, since your land slopes. Add a minimum of 1 foot of the same crushed stone (more if you can) over the perforated drain pipe. Fold the fabric to cover the stones. Continue the backfilling with coarse sand or bank-run gravel to within one foot of the top of the excavation and complete the backfilling with native soil sloping about 2 inches per foot. Plant grass on it; avoid shrubs or trees.

Safely installing a generator for back-up power

Q.    I live in the country and have suffered a number of power outages during storms, some lasting several hours. I am planning to install a generator in my garage to keep it dry and easily accessible. Do you have any recommendations on its installation?

A.    Do not install the generator in your garage or any enclosed structure! The combustion of any fuel-fired appliance generates deadly carbon monoxide. Install it outside and build a cover over it to protect it but leave at least two sides open.

Have a licensed electrician make the connection to your house wiring as it is absolutely essential that the generator be isolated from your power company lines with a transfer switch. Failure to do so can inadvertently send electric current back through the power company’s lines and that could kill a lineman working to restore the power who is under the impression that the line is dead.

Plywood soffit keeps buckling and peeling

Q.    The second floor of my 20-year-old house overhangs the first floor by two feet. Every few years sections of the plywood cover at the bottom of the overhang buckle and peel. I keep replacing them but would like to find a solution to this problem.
I have noticed that the Kraft paper of the insulation faces down. The insulation itself seems to be dry. Is venting required and how would it be done since the joists are perpendicular to the length of the house? Or should the insulation be turned over?

A.    No venting should be done. If you have noticed water stains covering the entire side of the plywood that is up against the insulation, you may have a condensation problem. It is probably due to warm, moist air from the first floor migrating into the overhang and condensing on the cold plywood.

The simplest solution, next time you have to replace a section of the plywood soffit, is to cut pieces of 1-inch-thick rigid insulation to fit tightly in each joist space and push them into the inside line of the first-floor wall. Then, caulk all four sides to seal the spaces. Turn the insulation over so the kraft paper is against the second floor subfloor but make sure that the entire joist spaces are filled with the insulation, even if you have to add some or replace what you have.

If you notice water stains concentrated on the outside edge of the soffit sections and fading as they progress toward the first floor wall, you may have a different problem. If you have ice dams at the eaves of your roof and you do not have a special waterproofing membrane under the shingles, there may be leakage into the second floor walls that works its way down to the overhang soffit. In that case, you should also have noticed some leakage at the window heads. This is obviously more serious and you should deal with it appropriately by either having Grace Ice & Water Shield (or equivalent) installed under the shingles or insulating and venting the attic to eliminate the ice dams. You should also make sure that there are no convective paths in the second floor ceiling that allow warm air to get into the attic.

In either case, paint the new sections of plywood on all sides before nailing them back in place.

Moisture-proofing a concrete-block basement

Q.    I would like to moisture-proof the basement to eliminate dampness and make the basement humidity the same as in the rest of the house. The house is 10 years old and has an unfinished basement six feet below grade. There are no signs of water seepage or wall cracks.

My plan is to apply two coats of Drylok, a rubber roofing membrane, and two layers of 6-mil plastic before studding, insulating and putting up drywall. Is this overkill? What is the best approach?

A.    Yes, I would say this is overkill. Since you mention that there are no wall cracks, I assume that your foundation is built with concrete blocks. Just in case you haven’t seen my oft-repeated discussions about the problems with waterproofing a block foundation from inside, be aware that doing so invites water to fill the blocks because it cannot leak into the basement. This water evaporates into the building and creates a very unhealthy environment that includes molds, mildew, a bad smell and potential deterioration of the framing and finishes. Years ago, I worked on an apartment building that had to be vacated for that very reason.

I realize that you haven’t had any moisture problems or leakage yet but that does not mean that you won’t. Once the water is in the blocks’ cores you won’t be able to get rid of it easily and you won’t even know it’s there until too late. You must also keep in mind that insulating the basement walls may mean that the ensuing deeper frost penetration will cause the walls to crack.

Insulating any foundation walls safely requires an effective drainage system (for protection if the proper grading fails or the water table rises), backfill of the foundation with coarse material that will drain efficiently and not expand in freezing temperatures; and positive grading to drain water away from the foundation. In the case of a 10-year-old house where you may not know if there is a functioning foundation drain and what kind of backfill there is, at least make sure the grade slopes away from the house.

As to the best way to finish the basement, tape 6-mil plastic to the walls no higher than 2 feet below the grade line and drape it onto the floor by 5 inches; this will ensure that if you ever have leakage at the base of the walls (where it usually occurs), water will not wet the studs and will seep under the plastic. If water seeps, this will tell that you have a grade problem. Nail a pressure-treated plate to the concrete floor through the plastic. Stud the walls, but only insulate them from the top to no more than two feet below grade; the heat loss through the bottom of the walls will help keep deep frost at bay. Keep the bottom of the drywall an inch from the floor and install a wood baseboard with screws for possible removal.