Low decks
A deck that sits too low to crawl under hides the sill and foundation behind it, right where mice run. If you can’t see under it, you can’t see the gaps.
At your house
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Where to look
- Decks too low to crawl under, so you can't see the sill and foundation behind them.
- The bottom edge of the deck, where it meets the ground, all the way around.
- Where the deck meets the house, along the board fastened to the wall and at both ends.
Sign to look for Burrows or worn paths along the bottom edge of the deck, and droppings where it meets the house.
The rule of thumb: if a gap is about the width of your finger, a mouse can use it.
Why mice use it, and the common mistake
Why mice use it
Mice like a sheltered run. Under a low deck they can work along the sill and foundation out of sight, and you can't get under to see the gaps or seal them.
Common DIY mistake
Screening only part of it, or leaving the top edge loose. Mice find the one open stretch, or push in under the loose edge.
The lasting fix
Screen the deck into the ground with 1/4-inch hardware cloth, all the way around, fastened at every point to the deck and the house.
Materials
- 1/4-inch hardware cloth, 19- or 23-gauge, stainless or heavy galvanized
- Exterior-grade screws or fasteners
- Tin snips, work gloves and a shovel or spade
Safety notes
- Make sure nothing is living under the deck before you close it in.
- Have buried lines marked before you dig.
The lasting fix, step by step
Walk around the deck
Look along the whole bottom edge, and at both ends where the deck meets the house. If you can't crawl under to check the sill and foundation, plan to screen it.
Use the finger test
Any gap along the bottom edge or at the house that's about the width of your finger or wider is a way in.
Screen it into the ground
Run 1/4-inch hardware cloth from the deck down into the ground, all the way around, so there's no open stretch and nothing can dig under.
Fasten every point
Fasten the hardware cloth at every point to the deck and the house, top edge included. A loose edge is a way in.
Materials
- 1/4-inch hardware cloth, 19- or 23-gauge, stainless or heavy galvanized
- Exterior-grade screws or fasteners
- Tin snips, work gloves and a shovel or spade
Safety notes
- Make sure nothing is living under the deck before you close it in.
- Have buried lines marked before you dig.
Before you seal the last gap
- Make sure nothing is still living inside. If mice are already in, set indoor snap traps along the walls as you seal, never as a substitute for sealing.
- Clear clutter and cardboard away from walls and corners, so there are fewer places to nest.
On a real house
Photos from homes we’ve inspected.
The same problem as a low deck: lattice looks closed from the yard, but every opening leads into the dark space behind it. 
Thin wire cloth with loose edges. Under a deck, use 1/4-inch hardware cloth screened into the ground and fastened at every point.
Related spots
Mice that use this gap often use these too. Check them on the same walk.
When in doubt, seal ’em out.