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Volume 6 Issue 9“Building Confidence”September 2008



Welcome to another newsletter where we build confidence for you to do it yourself.

Ask Away!

Here are some of the questions and answers for this month. Good questions, this month! I enjoy hearing from you all.

Hi Dave,
My question is about insulating under an exposed floor.
I have an addition on the back of my house that I am renovating, and I
need to insulate between the joists. When the addition was originally
built, three inches of insulation was attached to the joists, but never
covered with sheathing of any sort, and the elements have destroyed the
insulation, and the floor is ice cold in the winter.
The joists are about three feet above ground, and are exposed. Currently
there is only dirt under the addition, but I am going to pour a slab,
and then cover the openings with framed lattices, and use the area under
the addition as storage space for lawn equipment, etc.
My thoughts are to insulate with ten inches of insulation, and cover the
exposed joists with sheathing of some type. Plywood, osb, or something.
What about using plastic as a vapor barrier? Is this a good idea, or is
moisture build up a concern? What about venting, whether the plastic
vapor barrier is installed or not? Maybe I could vent the sheathing with
soffet vents, or something. I just don't want to leave the insulation
exposed like it was before.
What are your thoughts on this?

Hi Jim,

Sounds like a good idea to me. We don't usually worry about installing vapor barrier on a floor. It has to be on the warm side of the insulation, which is difficult for under a floor, with joists already installed. Usually, our flooring is considered a V.B. in itself. Don't apply any poly under the insulation on the cold side of the room, this will cause nothing but condensation problems. Like you suggested, just use a plywood, OSB, or solid boards below the insulation to hold it in place. Don't use a fiberboard as it will fall apart with moisture/humidity, eventually. A strip venting on each side of the bottom should work well with a strip of plastic flyscreen, used for soffit vents.


Hi Dan,
Just wanted to report a broken page on your website
[the error was immediately corrected by Dan, my brother and webmaster]

I have done some reading and found all your articles very informative.
I'm considering building a small mudroom addition on my house.  And I'm
trying to decide if I want to do much of it myself or hire a contractor.
I don't think I'll do the concrete work, but the rest I might.
Thanks for such a great resource.

Thanks very much, Dave!

Much appreciated.

I'm CC'ing my brother on this, so feel free to send him the specifics of your project and see what he says. He might ask you to become a Foreman member where you're entitled to unlimited answers as you work on your project [updated December 2009 to include ALL members], but that's a small price to pay for expert advice. Or he might just give you some advice for free since you helped us here!

Dave's brother and webmaster

Hi Dave,

I would also like to thank you for the nice comments regarding our website.

One of our purposes here is to Build Confidence in our readers to do the work themselves. We feel so strongly about this that we made it our motto. That said, doing it yourself is not for everyone. I was installing a counter top, I built, in a clients kitchen, a few years ago. I noticed that he had placed a chair in his family room next to the opening into the kitchen. He was watching a football game on his TV and watching me working at the same time. I was finishing up and about to present him with his invoice when I told him if I knew he was going to use me as entertainment for the day, I would have charged him more. He laughed and got real serious, telling me he is not handy at all, but loves to watch the TV home channels and envies the guys, like myself, who can do these projects. I love to receive emails from our readers who get the enjoyment of building a certain project and the satisfaction of doing it themselves.

I'm not contracting anymore, but you can imagine, I'm pretty busy answering people's questions and I take it very seriously, sometimes spending a lot of time clarifying the situation and making diagrams that help make my answers clear. We feel that this is a very valuable service and we decided several years ago that it was only fair that we charge extra for it. That is why we created the Foreman level of membership. For a little bit extra per year, you can have a direct communication line to me to take the time to make sure your questions are fully answered with diagrams if needed.

Naturally, I'll answer quick questions from non-members. We also have a free newsletter that we put out every month, based on the questions and comments I get from our readers and members. I encourage you to sign up for our newsletter. You can view these by clicking on:

If you are serious about doing some of the projects around your home yourself, we are here to help. Read our articles on the subject, go over the questions already asked and answered under the different topics or search the newsletters or articles using keywords on Dan's search engine on the top left of every page. If you have a question, by all means send me an email. I don't get into engineering questions or estimate the cost of projects, but will point you towards an answer to most construction queries.


Hardwood in Dining Room.  Ceramic Tile in Hallway. Where do you stop the
hardwood; inside the doorway or outside the doorway?

The joint should be under the center of the door. If just an opening, in the center of the opening.


Looking for a fairly simple (DRY SINK) that I can build to house my
plants for winter in my sunroom.
By the way.......I am 73 yrs old and build all sorts of things.  Many
outside furniture items, bookcases, all sorts of shop cabinets, etc.  OH
did I mention??? I am also a woman!  I sided our cabin. built the decks
and stairs, installed an upper level inside the cabin that had a 23 foot
ceiling.. covered all the dark log walls with knotty pine...installed
wainscot, and renovated the entire kitchen where we now live.


Hi Dee,

Thanks for the email, got a kick out of it. Glad you have at least two things going for you - 73 years old and a woman!!

Sorry I'm so stupid, but what's a dry sink? Could you elaborate a bit. I'm not into the gardening scene. I'm sure we can work something out though.


I never heard anymore from Dee. I was looking forward to learning all about a dry sink. Oh, well!

Dave, Just wanted to send you a few photos of the finished workshop I built
with the plans you drew for me last fall.  As you can see it ended up
matching the existing garage nicely.  Needless to say, I couldn't have done
it without your help.

Wow! Thanks, Jim for the pics. The shop looks great, very nice job.

I'll get Dan to put them on our site.


[You can see Jim's photos here.]

I just read the article on installing an inside handrail and plan on
using your great site when I finish this project- thanks for this site!
My question is this- I also want lino/ sheet vinyl for the floor there,
do I do the flooring first or second?  I'm taking out a pony wall,
so there is finish flooring (carpet) up to where the railing is to be.
In the article, I saw that hardwood and carpet were addressed,
but didn't catch any reference to vinyl or tile.

Hi Tammy,

With lino around the stair opening, I prefer putting in the newels first, in case I run into a problem putting the newel through the floor. If I hit a double floor joist or something like that and want to move the newel slightly and the lino is in place, I have a hole in the lino. It is easy to install the lino after the newels and spindles are in place. Come up to the bottom rail with the lino or vinyl and install a shoe molding against the rail to hold the lino down.

Here is a drawing of a shoe mold:

It comes in hemlock or oak, as do the handrail parts.

Hope this helps,


Hi Dave,

Every source seems to recommend T&G plywood for subfloors.
However, I live in France, and T&G plywood is not available here.
The choice is T&G OSB or "plain" (not T&G) plywood. Which is the
better option? And what thickness would you recommend?
Or is T&G plywood so much better than any other option that it
would be worth taking 60 sheets of plywood down to a sawmill and
getting them to cut tongues and grooves into it?!
Built your 10' x 12' gable-roof shed last year, initially as a
site hut for while we're building our real house. Later we'll add
windows and make it our garden house. It's been a real blessing --
so much more pleasant than huddling under tarpaulins during
hailstorms, and having to cover all the materials and equipment
with tarps every evening! This was the first time we'd built any
kind of structure, and we were delighted with how it turned out.
Since added your workbench. Both have elicited compliments from
people impressed that things so good could be so simple.
Used 18 mm T&G OSB for the shed, which works fine (like, it hasn't
collapsed under my weight so far!), but of course I'm less fussy
about my garden shed than I am about my home, hence my wanting to
check this point.
All the best,

Hi Steve,

Thanks for your email and most excellent question. I'm glad our website has been helpful to you and to hear from a member from France.

Your question regarding OSB and plywood for subfloors is a very controversial topic. With your comment of taking 60 sheets of plywood to get milled, I get the sense of you not understanding the reason for the tongue and groove on a 4x8 sheet of plywood or OSB. Let me explain.

Plywood and OSB are both engineered panels. Plywood is made up of layers of wood veneers glued together, with the direction of the grain in alternate layers at 90 degrees to each other. OSB, oriented strand board, is made up of strands or small strips of wood, glued together in layers, with each layer generally oriented at 90 degrees with each other. Each product has mainly 2 grades for subfloors. Plywood comes in a standard sheathing, as well as a select sheathing grade. The standard sheathing has loose knots, including knot holes in the top veneers and the select has solid knots and no holes or very small ones. Both grades come with a tongue on one long side and a matching groove on the other long side. The ends are square. The standard grade is used for most applications of subfloor such as under carpet, hardwood, ceramic tile, etc. The select grade is chosen for under a vinyl decking material. An underlayment should be used under vinyl sheet flooring or tile. OSB also comes in 2 grades, the standard OSB and the enhanced OSB with more glue and resins to lower the chance of edge swelling.

Engineered panels both have advantages and disadvantages. Where the controversy comes in is with the OSB and its swelling under humid or wet conditions during the building process. I don't know what the humidity is or amount of rainfall in your area. In my area, the West Coast of Canada, we have 100% humidity in the Winter and high humidity during the other seasons. High humidity and wood products don't go well together. We have problems with mold in our homes, but have means of solving these problems by following guidelines in our building codes. I built my home in 1992 and having worked with OSB subfloors before, chose to go with plywood. I used solid 1x8 re-sawn boards on most of my walls, after using them for forms. Since I did all the forming, framing and finishing work myself, saving time in labor was not an issue for me. I used OSB panels on the roof. These were not T&G.

My personal reasons for going with plywood rather than OSB are as follows:

  • With our humidity I notice that when placing a 2x4 against the tongue side of the sheet and hammering the sheets together, it mushrooms a bit. This makes it labor intensive to fit the tongue into this mushroomed section.
  • Our house has alot of hardwood nailed to the subfloor. OSB was not recommended at that time for holding nails well. This is before enhanced OSB.
  • The cost difference between plywood and OSB was not that substantial in the overall cost of building a house.

Now to explain why the tongue and groove is on a sheet of plywood or OSB when used for a subfloor. Since plywood goes across the floor joists with its long dimension, the ends are supported on joists, but the sides are between the joists, unsupported for 14 1/2 inches. When walking on the floor between these joists, at the edge of the panel, you can feel the deflection of the edge of the panel. The tongue and groove tie the sheets together eliminating the cost of labor and material to install blocking at 4 foot intervals, between each joist. I realize that you were probably over reacting with the plywood to the mill scenario to make a statement, but as explained above, you have another option of using square edged plywood with the installation of blocking.

Would I use OSB for subfloor? Under different circumstances of less humidity or of framing in the Summer with no chance of rain, yes I would, especially if I couldn't purchase plywood or the cost difference between the two was too great. In your email you mentioned using the 18mm thickness of OSB which suggests that this is the enhanced grade of OSB I mentioned. I came across a website which addresses this question in discussing a swelling test that they performed comparing plywood with the 2 OSBs at:

Well, Steve, I hope I've helped a bit with your hesitation to use OSB for subfloor. If your area has relatively low humidity and won't get wet during construction you don't have an issue. If on the other hand, your area is like mine with high relative humidity, you may want to think twice about using OSB. You now know of another way of installing subfloor panels without the advantage of tongue and groove construction.


Hi Dave,
Many thanks for that detailed reply.
While I did understand the damp/swelling issues related to OSB,
I hadn't twigged that the purpose of using tongues and grooves was
to reduce bending along the joins, between joists. Thanks for
filling me in on that. This being the case, blocking would clearly
achieve the same result as T&G, but with a fair bit of extra work.
The OSB I used for the shed floor (which in France is T&G along the
short sides, as well as the long ones) reacted surprisingly well to
being out in the rain for the few days that elapsed between my
building the floor and getting the roof on (this was the first time
I'd cut and installed rafters, and it took me forever!). It did swell
slightly, but it went back to normal once it dried out, and anyway,
by then it was already in place. Since I was working in summer,
and I'd stored it under a tarpaulin, it was good and dry when I laid it,
so there was no mushrooming when I hammered the edges through a 2 x 4.
I even found that if I was careful I could hit it moderately hard with
the hammer direct!
So since I have no desire to install blocking (it would "block" my
pipes and cables, apart from the time and effort required to install it),
but do not want to get seasick as I walk across my living room,
I guess it's going to be OSB.
Thanks again for your help .. I'll doubtlessly be calling on you again
as the house progresses, and we move from building the basement to
installing floors, partitions, doors, etc.
All the best,

Hi Steve,

I think you have made the best decision in your circumstances.

One point about the blocking, I should mention. The blocking can be 2x4s on the flat, which would not affect piping, etc.

I looked at the Picasa site - looking good! Great view, too!


Well, that should do it for this month. I hope this has given you a bit of confidence to tackle at least a small project so you too can have the tremendous feeling of satisfaction as these writers have.


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