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What fails on a house, why it fails, and what it should cost

Home/Siding/Gaps at trim

Siding · You can handle this one

Gaps at trim and penetrations

Caulk at windows, doors and utility penetrations is the main water and pest barrier. Inspecting and renewing it every year is inexpensive and prevents most siding failures.

Quick answerEvery place something passes through or meets the siding, such as window and door trim, hose bibs, dryer vents, electrical boxes and cable lines, is a joint that has to be sealed. Caulk shrinks, cracks and pulls away with age. Walk the house once a year, cut out failed caulk and reseal. It’s cheap, it’s a Saturday job, and it prevents most of the water damage we see behind siding. You can handle this one yourself. No call needed.

Siding sheds water well across its face. It’s the edges and holes that leak. Most soft walls, peeling paint and pest entries trace back to a gap at trim or a penetration that nobody resealed.

1Why the gaps open up

  • Caulk ages. Sun and temperature swings make it harden, shrink and crack.
  • Materials move. Siding, trim and windows expand and contract at different rates and pull joints apart.
  • New holes. Cable, satellite, solar and security installers often drill through siding and seal poorly, or not at all.

2How to check

  1. Walk the houseLook at every window and door perimeter, corner trim, and every pipe, vent, wire and box that passes through the wall.
  2. Press the caulkGood caulk is still flexible. Cracked, hard or peeling caulk needs replacing.
  3. Look for daylight and pestsGaps you can slide a card into, insect trails or nesting debris mean an open joint.
  4. Check the wood nearbyProbe trim near any gap. Soft wood means water has already been getting in.

3Fixing it

Do it yourself

  • Cut out old, failed caulk with a utility knife or scraper
  • Clean and dry the joint
  • Use backer rod in deep gaps before caulking
  • Use an exterior sealant rated for your siding and trim
  • Seal around penetrations with the right cover or flashing block where one exists

Hire a pro

  • The wood behind the gap is soft
  • Window or door flashing is missing
  • The joints are on a second story
Don’t seal everything

Don’t caulk the bottom edges of lap siding or block weep holes in vinyl. Water that gets behind the siding needs a way out. With vinyl, don’t caulk panels tight into the trim channels; they need room to move.

Older houses

On a pre-1978 home, scraping old paint near the joints can release lead dust. If you pay someone to do it, hire a lead-safe certified firm. If the siding might be asbestos-cement, don’t scrape or drill it.

4What drives the cost

Doing it yourself costs a few tubes of sealant and an afternoon. Hiring it out costs more with height, the number of openings, and any rotted trim found along the way.

Siding cost

5Questions

How often should I recaulk?

Inspect every year and replace whatever has failed. You won’t need to redo every joint every year.

Can I caulk over old caulk?

It won’t last. Remove the failed caulk first so the new bead bonds to clean surfaces.

What about the gaps where vinyl meets trim?

Those are designed to let vinyl move. Don’t caulk vinyl panels tight into J-channel.

Written by Jaylan Jones. I Like To Exterior Services earns a referral fee when a call connects to a contractor. See our business-model disclosure.