Building Confidence

Volume 16 Issue 10
ISSN 1923-7162

Welcome to Dave's Shop Talk's Home Improvement Newsletter of questions from our members on their construction projects, a Tip of the Month and a home remodeling article, both from our website at

Tip of the Month

Pex piping is a good alternative to expensive copper pipe in a home renovation. Adapters from copper pipe to Pex are available. Fittings are either screwed on or crimped on.

And a Bonus Tip:

Use inexpensive plumbing strapping for holding pipe and valves onto wall framing.

Ask Dave!

Hi Dave what do you recommend for a vent (plastic, metal, size?) for pony walls in a crawl space foundation, and how do I install a vent in a 2x6 pony wall with studs on 16" centers, and fiberglass insulation? Do you also recommend a window? Thanks

Hi Andy,

Vents in a crawlspace are required by the building code, unless the crawlspace acts as a warm air plenum for the furnace. Otherwise, you need vents. These are very simple, plastic vents that open and close by sliding them horizontally. They fit into a 14" space, so they don't need special framing. They should be across from each other and spread out so there is good cross ventilation. There is a simple formula which helps you know exactly the number of vents to put in a crawlspace, based on the area of the floor in the crawlspace. The vents required in a non-heated crawlspace is not less than 1 to 500; vent area to floor area.

In your case: 33' x 24' = 792 sq.ft, you need 1.6 sq. ft of venting. This works out to about 4 vents, spaced out on the 33' walls. I would suggest coming in about 8'- 3" in from each end at the center of the vents, leaving a 16'-6" space in the middle. You don't want too many vents to freeze the pipes in the winter. You can either frame the vents or cut the insulation out on the bottom of the vents and let it just lay over the vent in the winter. In the spring, each year, fold the insulation back out of the way of the vent and slide it open from the outside. Depending on your temperatures where the cottage is, you may need to have electric heat under the pipes to keep from freezing. Get the base board that has a thermostat built in. Remember to frame in an access door.

When installing the plumbing, don't run your supply line in from the end and laying in the crawlspace. Bury it under the slab then come up right in the middle of the plumbing area. This shortens the exposed plumbing from freezing problems.

No, I don't recommend windows in a crawlspace. I feel it would be a waste of money in a 3' high crawlspace.


Thanks for all the great advice Dave. What is your recommendation for insulating under the main floor in the crawl space? I was thinking that if possible I could install insulation during the build from the top of the joists, which seems to me would be easier than installing insulation from under the floor after the sheeting is installed. Thanks Andy

Hi Andy,

Installing insulation before the sub-floor is a good idea, if it doesn't rain. Don't make the mistake of applying vapour barrier, the floor doesn't need vapour barrier. The carpet or lino becomes one. Also, put strips under the joists to hold the insulation in.

Another thought: do you really need to insulate the floor if the perimeter is insulated? Will you be using this cottage in the Winter?


Hi Dave yes we are planning to use this in the winter. I have enough tarps for the subfloor in case of rain or snow in the next 6 weeks. Do I need to use paper back fiberglass insulation in the floor? So I don't need a vapor barrier on the crawl space side of the subfloor? Thanks

Hi Andy,

No, don't use any vapor barrier on the bottom of the joists. That is a big mistake lots of guys make. VB has to be on the warm side of the insulation or it creates condensation. Use regular, non-paper backed fiberglass insulation.


Dave I am planning on building the pony walls and then sheeting with full 4x8 treated plywood after the floor joists are in place. Do I need a vapor barrier on both sides of the insulation in the pony wall? Thanks

Hi Andy,

No, you want the vapor barrier on the inside - the warm side and breathable tarpaper - 30 or 60 minute, or Tyvec or Typar on the outside, between the framing and the siding. You never want to enclose a wall in poly where it cannot breathe.


I thought so but as I am sure you know Dave there are many, many opinions out there, most of them unsolicited. Thanks for the guidance. Andy

Thanks, Andy, keep 'em coming! Every question you have, there is probably 100 out there wondering about the same thing, but too bashful to ask.


Hi Dave how do I build an access door/panel in the floor for crawl space access? The plans call for an opening in the floor joists, but I am not sure how to build the access door. Thanks

Hi Andy,

The crawl space access must be at least 20x28 inches. Here is a drawing of the access in a floor:

Diagrem showing where to install joist hangers when making a crawl space access hole in the floor.

Double up the joists on each side of the opening. Frame in the opening with joist hangers to the double joist, to support the sides of the opening.


Thanks Dave - how does the double joist work with engineered floor trusses?

Hi Andy,

Engineered floor trusses is a totally different thing. You need to contact the engineers you bought these from and they will tell you what needs to be done. Otherwise, you lose your warranty if you start cutting these trusses.


Hi Dave for my pony walls do I need pressure treated or PWF lumber? What's the difference? Thanks Andy

Hi Andy,

PWF or permanent wood foundation is made from pressure treated dimension lumber and plywood. If the pony wall acts as a retaining wall for backfill it needs to be a PWF. If siding is attached you need the bottom plate (PTW) pressure treated wood, or standard lumber with a sill gasket under it.


Dave what is the nailing pattern required for laminating the LVL beam? Thanks

Hi Andy,

The nailing pattern, size and spacing of the nails, should accompany the beam in the Specification papers from the Engineer.

Hi Dave what caulking should I use between the wood pony wall bottom plate and the concrete slab? Thanks


Usually, we staple the sill gasket to the bottom of the plate. This keeps it off the concrete as well as forms a gasket between the uneven surface of the concrete and the wood. We do not need to caulk the bottom plate, if you follow these procedures. The bottom plate should be flush with the edge of the concrete slab. The siding is nailed to the bottom plate and extends below the plate, overlapping the concrete joint, so this method keeps any moisture out.


You can see that Andy has been busy the last month, or so. He writes, "we are building a new cottage on our lot at Lake Winnipeg. I have ordered a prefab. It is just over 1000 sf including a 250 sf loft. I just got the building permit after getting the foundation and structure plans, engineer reviewed and approved (as required by the local authority having jurisdiction). I am making a choice for foundation contractor. The foundation is thickened edge slab on grade, with 36" wood pony walls (for the crawl space), and an LVL (3 ply) 5-1/4x9-1/2 1.8E 33' center beam with teleposts. The prefab comes with 24' x 2 x 11-7/8" TJI engineered wood floor joists. It also comes with 4 - 12' x 11 7/8" - 2x6 end gable pony walls. I am planning to build the 2x6 PT pony walls myself. So from the end there will be concrete slab, 36" PT 2x6 pony wall, and 2x6 end gable pony wall."

Andy is going about his project the right way: using the internet for ideas, going with a pre-fab package, including proper plans, getting a building permit and getting proper engineered beams, getting a contractor for work he is not comfortable in doing himself, getting advice and asking questions.


Feature Article of the Month

(taken from our website:

Deck 1: Raised Backyard Wood Deck

Most houses today come with a raised backyard wood deck or balcony built off the kitchen or main floor level, raised 6' or 8' off the ground. This is the best place for the family barbeque, close to the kitchen. If you own an older home and always wanted to build a raised backyard wood deck, let's get started.

I designed a raised backyard wood deck 12'x12' to use as an example.

Attaching the Raised Backyard Wood Deck to Your House

On the house side of the backyard wood deck you have the option of using a ledger board as a box joist. This board is bolted to the box joist of the house with 3/8" x 4" lag bolts with two rows every 16" apart, or using a beam with two posts right up against the house. If the ledger board is your option, the stucco or siding should be removed and the 2x8 ledger attached directly over the sheathing into the studs or existing box joist. I prefer the ledger board, myself, since it ties the raised backyard wood deck into the house preventing any movement of the deck. It is easier to prevent leaking through when the raised backyard wood deck is attached, as well. The 2x8 ledger should be kept 2" lower than the top of the existing box joist on the house. The joists are then attached to this ledger with joist hangers. Layout the joist hangers, first before drilling the lags, so they won't be in the way of the hangers.

Diagram an elevated deck or balcony floor plan showing box joist, beam, floor joists and post with measurements.

The Footings of Your Raised Backyard Wood Deck

After installing the ledger, layout the position of the footings and concrete columns of your raised backyard wood deck, keeping in mind the depth of frost. A stake in the ground or erecting batter boards are good ideas to help get the excavation square and accurate. For more info about batter boards see my article How to Build a House 2: The Concrete Foundation

Form and pour the concrete, insert the post saddle into the wet concrete, ensuring it is level. Strip the forms in a day or two and start building the posts and beams of the raised backyard wood deck. A triple beam made up of 2x10s gets pretty heavy after a few feet long. I usually build a beam like this in place, especially when working by myself.

The Posts of Your Raised Backyard Wood Deck

Get the height of the floor of your raised backyard wood deck from the ledger board on the house. The height of the posts can be calculated by leveling over from the house to the post saddle less the thickness of the beam.

Usually a raised backyard wood deck such as this has a slight drain, unless covered with a roof. Figure about 1/4" per foot, so that is 3" in 12 feet. Cut the post off another 3" for runoff.

Temporarily brace up the posts of your raised backyard wood deck to stakes driven into the ground. Nail the beam together using 3" common galvanized nails, two rows every 16" apart. Toe-nail the beam into the post, as well, according to the drawing of the raised backyard wood deck. Use a 2x4 or 2x6 cleat or scab over the joint of the beam and post, with a 45° bottom cut, nailed with 3" galvanized nails, too. Square up the beam with the house by carefully measuring the width of floor on each end and then the diagonals, making them the same length. Add further braces, if necsessary.

The Floor of Your Raised Backyard Wood Deck

Install the 2x8 floor joists of the raised backyard wood deck laying them into the hangers on the house end and 16" on centers on the beam. Toe-nail them into position on the beam from each side of the joist. Nail the outer box joist into position, tying the floor of the raised backyard wood deck together.

Use a sheathing of either 5/8" tongue and groove select plywood, if finishing your raised backyard wood deck with a vinyl decking, my choice, or with 2" decking lumber, (5/4" is acceptable, too). When nailing the sheathing to the floor of your raised backyard wood deck, place nails at 6" along the edges and 12" in the center of the sheet, using a construction adhesive, as well.

If vinyl decking is chosen for your raised backyard wood deck, to be able to make use of storage underneath, talk to your decking person. Some require a cant strip along the house, on top of the sheathing. This enables the vinyl to wrap up the vertical face of the house without an extreme bend. Other vinyl installers just bend it up the wall without a worry. My vinyl decking was installed on my raised backyard wood deck without the cant strip, to my surprise, but without a problem for 13 years. I live on the South West Coast of Canada, where the weather temperatures are not that extreme.

Diagram of deck support showing joists, beam, scab, post, post saddle, concrete footing and column, grade and rebar with measurements.

I'll continue with how to build a deck railing for your raised backyard wood deck in my next article.

Check out these drawings and get back with me for any other questions.

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(Ask Dave) (About Dave)

Your source for building tips, woodworking & furniture plans, house plans and building advice directly from Dave...

Hi, I'm Dave Osborne. With over 50 years experience as a journeyman carpenter, foreman and contractor in heavy construction I enjoyed working with apprentices and sharing the tricks of the trade that others shared with me. Now I get emails from Members all over the world and we include many of my answers in our Free Monthly Newsletters. Some of my answers include drawings and instructions specific to a project, but may also answer your questions. I use correct construction terminology, so you can confidently inform your building supply dealers or contractors exactly what you need.


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