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How to repair a leaky chimney – Part 2

Bob Jackson
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by Bob Jackson

How to repair a leaky chimney – inspect the chimney box in the attic to identify the source of the roof leak and setting up roof brackets to get on the steep roof.

This project is continued from Part 1.

The leak in the attic is coming from the bottom corner of the chimney box, but before going up on the roof I decided to take a closer look inside the chimney for evidence of the leak since water flows downhill and the leak has to be originating somewhere higher up. The chimney cap looks great and I saw no evidence of a leak on the chimney box walls.

Inspecting the Chimney Box for Leaks
Inspecting the Chimney Box for Leaks

Chimney Box Leak Inspection

One particular 2×4 stud inside the chimney box had what might be severe water stains – or it could be nothing more than a pine sap pattern in the wood grain – it was hard to tell. It felt dry but it may be wet under the surface of the wood. I was suspicious because this stud is near the corner where the leak is occurring and water could be wicking under the 2×4 sole plate making it’s way to the corner.

Possible Water Stains on 2x4 Stud of Chimney Box?
Possible Water Stains on 2×4 Stud of Chimney Box?

The dark pattern runs up the stud towards the chimney cap, but ends before reaching the top.

Water Stains on 2x4 Chimney Box Stud?
Water Stains on 2×4 Chimney Box Stud?

The dark pattern is only on this side of the stud, but water can trickle down and follow a strange path.

Roof Leak Testing with a Moisture Meter

Short of waiting for the next thunderstorm, the only way to really know is to test the wood with a moisture meter, so I bought the General Tools MMD4E Digital Moisture MeterHand Tools) for $32.98 (battery included!) from

General Moisture Meter - Moisture Seeker Model No. MMD4E
General Moisture Meter – Moisture Seeker Model No. MMD4E

The MMD4E Moisture Meter is easy to use and has two different settings: 1) wood and 2) construction materials (concrete, brick, drywall, carpet, etc.). It has a “hold” button to freeze a reading on the display in case you’re making a measurement in a tight spot where you can’t see the display. The meter beeps as it’s takes a reading to let you know when the reading is stable. A percent moisture table is on back of the meter for quick reference – a nice touch so you don’t need to carry around the manual.

I set the moisture meter to the “wood” setting and pressed the two needle probes into the 2×4 stud in the darkened area. The wood stud was very dry at 5.3% moisture content. The dark area on the stud is therefore not caused by a chimney leak.

Chimney Leak Testing with a Moisture Meter
Chimney Leak Testing with a Moisture Meter

I checked several spots on the stud, the OSB sheathing, joists and rafters inside the attic; everything was consistently reading 5% to 6% moisture content. For comparison, my wood deck read a 7.1% moisture content.

Steep Roof: Brackets and Ladders

Having finished the attic inspection, I needed to get on the roof to inspect the chimney to find the leak. I don’t like working on steep roofs and especially the high and steep 12×12 pitch roof on my house. A 12×12 roof slopes at a 45 degree angle because it rises 1 foot for each foot of horizontal run.

I’m very safety conscious (meaning worried) when getting on the roof, so I took time to prepare by:

  • Screwing a 2×4 stop to the wood deck to brace the feet of the 24 ft extension ladder.
  • Install two roof brackets with a 2×6 step board. Each bracket is slipped under the shingle and fastened with three (3) pan head wood screws. (The screw holes under the shingles will be filled with roofing caulk when the brackets are removed.)
  • A second 16 ft extension ladder is laid on the 12×12 pitch roof against the 2×6 step board.
  • The 16 ft ladder is tied off to another roof bracket to prevent it from sliding sideways. The extra roof bracket also serves as a handhold for getting on/off the hip roof.

You might want tie the 24 ft extension ladder to the lower roof bracket above the gutter so there’s no chance of it falling sideways and leaving you stranded on the roof. I didn’t tie off the lower ladder because the deck is level and I always had my son with me on the deck.

Working on a Steep Roof: Ladder and Roof Brackets
Working on a Steep Roof: Ladder and Roof Brackets

View of the 16 foot extension ladder laying on the 12×12 roof and tied off to the roof bracket. It’s very easy to climb up the roof with a ladder this way. Note that both sections of the ladder are tied together because the extension ladder will easily separate in two pieces if pulled. I used an Anchor Bend knot to tie the rope with a finishing half hitch because this knot is easy to tie and secure.

Working on a Steep Roof: Ladder Access
Working on a Steep Roof: Ladder Access

The satellite dish prevented placing the ladder closer to the chimney. It looks like a long ways down because it is!

Working on a Steep Roof: Ladder Supported by Roof Brackets
Working on a Steep Roof: Ladder Supported by Roof Brackets

This project is continued in Part 3.

Take care,

Bob Jackson

chimney boxchimney leakmoisture meterroof bracketroof leak
Bob Jackson
Bob Jackson
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