Deck footings: How low should you go?

Frost depth a key factor in structural design

By Inman News Feed
Add Comment Add Comment | Comments: 0 | Posted Apr. 27, 2012

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Frost depth a key factor in structural design

Paul Bianchina
Inman News®

Q: How do you determine the depth of the deck footings to assure you have gone below the frost line? I live in central New Jersey, and thought I've always heard that the frost line here was 18 inches. But from reading a few articles on decks, I've seen conflicting information. Do you have a reliable resource? --Frank G.

A: As you can imagine, frost lines vary widely by region. Also, most codes require that your footings be an additional 12 inches below the frost-line depth, as an added precaution against rare deep-freezing conditions. So, your best bet is to simply call your local building department and ask.

However, if you would like to try to figure it out yourself, there is a good booklet available for free from the Department of Housing and Urban Development (HUD). Go to In the search box, enter "Structural Design Loads for One- and Two-Family Dwellings," which will take you to the booklet. It's about 50 pages, in PDF format, so you can read it online or print it out. You can also order a copy from them if you'd prefer.

Q: We currently have a wood-burning fireplace and electric heat and a heat pump that work fine but are 20 years old. We are thinking that we would like to replace them with a new electric furnace and heat pump when the time comes, but would like to wait until the electric furnace gives out. In the meantime, we would like to install some kind of heating device in the fireplace.

We don't know if we should go to the expense of having gas installed so we can have gas logs installed in the fireplace or do as a neighbor has done and have a propane tank installed in the yard to supply logs to the fireplace. We know the gas company will cover the cost of installing the gas line only if we change three or more appliances. Any suggestions? --April E.

A: It depends a lot on exactly what you're trying to accomplish. Adding a vented gas log set to your existing wood-burning fireplace will get you the convenience of watching a fire without the mess of wood, but it won't do much for heat, since a large amount of the heat generated by the gas logs goes straight up the chimney. If you're looking for the convenience of being able to start wood with a gas lighter, then a small propane tank installation plumbed to a gas log lighter will do the trick.

If the goal is more heat, then you have a couple of options. You could install an airtight wood-burning insert in the existing fireplace, which still burns wood but does it more efficiently, and doesn't require any gas connection. Or you could have a sealed gas insert installed in the existing fireplace, which is easier and cleaner to operate than a wood-burning one and produces more heat, but requires propane or natural gas.

As to which gas source to use if you go that route, it depends on the cost. You would need to talk with the gas company about how much a meter would cost to install with only a single gas connection, as well as a plumber to determine the gas line costs. I suspect propane might be less expensive, but you would also need to talk to a propane company. If you don't like the looks of an exposed propane tank, you can have an underground tank put in, but that adds the cost of excavating.

A lot of this also depends on the condition of your existing fireplace, and whether it's in good enough condition to accept an insert. So all that being said, I would start with an experienced, licensed fireplace company and have them come out, inspect everything, and help you out with some options and cost estimates.

Incidentally, if you are doing this to save on your electric bill by not running your furnace as much, you would need to look at the cost trade-offs -- electricity savings versus installed cost and operating cost of the new gas unit. It's doubtful you would see any kind of financial payback within any reasonable time frame.

Q: We live in northeastern California. In 2002 we had our home constructed. This year we have decided to merely "cover" the existing small wire mesh [foundation vents] with something that can be removed in the summer.

Both my husband and I, have in our mind's eye, a removable-type vent (my eye sees a little wing nut type, wooden frame with a small wire 1/8-inch square mesh encased in a plastic material-type thing that you can turn to release the cover for storage. I can't imagine what my husband sees!) In any event, we can find no such type of product. We have approximately 30 vents to cover!

Internet searches reveal: flat 4 screw-type covers you leave on (don't want that); then there are louvers (don't want that); then there is one that appears to have a concave appearance (not exactly what we're thinking of either). Do you have any idea of a "plan" so that hubby can build them out of a wood frame, plywood or other material? Or where we can find something described that we have in mind? --Jacquelynne M.

A: I don't really have much to offer you in the way of plans. However, because your house is fairly new, I'm assuming you have standard foundation vents -- a grey or black plastic, screened vent set in the concrete foundation wall. There are white foam blocks that are made specifically to fit in those vents and seal them off, and that's what most people use for this purpose. Cost is typically around $1 each. Just press them into the vent at the start of winter, and pull them out again once the threat of freezing weather is past. They're reusable, and will last quite a few seasons.

Remodeling and repair questions? Email Paul at All product reviews are based on the author's actual testing of free review samples provided by the manufacturers.

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