Q. We converted a small laundry room off the kitchen into a closet. All pipes remain. Periodically a very strong sulfur odor fills the room. Any thoughts on possible sources of this odor?

A. I think you left the drain for the washer's discharge hose open. It's the hole in the middle of the washer hook up indented into the wall with the hot faucet on the left and cold on the right. The drain has a plumbing trap under it that has since drie d out and instead of a drain it is now a vent and from time to time it will act like a vent and expel some "air" into the room that is tainted with the smells of plumbing waste you interpret as sulfuric. It's probably 1-1/2 inch waste line-- measure it across the opening at its widest point to confirm that. Go to the hardware store and get a neoprene plug that size with a stainless steel wing nut in its center so when you tighten the nut the plug expands creating a very tight fit in the top of that dr ain line. Install it, tighten it and the smell will go away and not return.

Q. I have a one storey house with a flat roof. The only space between the drywall ceiling and the plywood roof is the depth of the roof joists that are 2 by 10s with 11 feet of span from house edge to interior bearing walls. The finished roof is tar and stone. The roof is out of level. The rear line at the center point is low. The front line at the left corner is lower and side lines are as bad. My intention is to leave this roof “as is” and build a knee wall probably 12 to 16 inches high around the perimeter to establish a level area to support manufactured A frame trusses for a 5/12 pitch roof. I intend to have an 18 inch overhang on each side with ventilation at the overhang’s soffit and as well as a vent at each gable end.

I have been in this house over three years with no sign of a leak and the roof appears in very good condition as are all ceilings. The house is about forty years old but the roof, I have no idea, but surely not forty years old.

Is there a possibility of hidden problems such as condensation, dampness, mold or anything else that you would expect? Secondly, should I insulate between the new trusses or flat on the existing roof or no new insulation at all?

A. I have a couple of suggestions to offer in addition to the concerns you’ve raised. You seem house building savvy as your question is peppered with carpenter language so as we go along considering your questions I’ll try to put things understandable f or those still reading.

It appears the original builder of your abode built low areas into this roof that bother you for the purposes of drainage. Nature hates truly flat roofs and punishes anyone foolish enough to build them and some knew that forty years ago. What you are pro posing to do is essentially put a hat on your house, taking it from the realm of the pill box to the look of a Cape Cod style cottage. You wont regret it. Leveling the perimeter with a knee wall before setting pre-engineered roof trusses is the way to go .

I did the math and discovered that with an average 16 inch perimeter knee wall, a knee wall is a wall that is not full height, your eighteen inch overhang will place the soffit-- the underside of the overhang-- about seven and half inches down from the t op of the knee wall in a roof that rises five inches per foot of horizontal distance covered to the center of the house-- a 5/12 pitch. That places the entire new assembly above the old roofline.

I am concerned about the best method of attaching this structure to the old so when the next storm with a name comes along you don’t come home to find your new roof out in the yard. I’m not a structural engineer but I am an old house carpenter and know when to seek the counsel of such a person and in this situation I strongly recommend it. You want to attach this structure using best practices and it behooves you to seek those out. Sure, you’ll need a building permit and it will have to be built to cod e but remember codes are minimum standards and you might want to exceed them here.

As for future moisture problems remember that at the very least a roof is a moisture barrier. I have no idea to what degree the space between the ceiling drywall and the flat roof is currently insulated-- but that’s where to concentrate any insulation ef forts. The attic space that you will create we know as a “cold roof”. A cold roof is designed to, through ventilation, maintain a temperature close to the outside air. Notice in winter when you drive around after a snowstorm and see snow still on some roofs. Those are cold roofs doing what they are supposed to do. The insulation should be just above the spaces heated and cooled-- known as the building envelope. That’s where it is now. If you place insulation above and on top of the old roof you wil l be creating a condensation plane that could cause you trouble, so don’t do it. Also your roofer will want to install a ridge vent along the peak of your new roof and that’s a good idea. Then you can dispense with the gable end vents as not only being unneeded but, we have learned, counter-productive with ridge and soffit venting.