Repair detail of rotting timber wall plate and roof rafters? 2

[Redacted]

Hi there,

I am working on a project, which involves quite an old home. After doing an inspection of the roof structure it was found that some portions of the ends of the rafters and a portion of the timber wall plate, which rests on the load bearing walls/beams has rotted.

What is the typical detail for fixing these kind of issues?

See the attached image.

For the timber wall plate, would you cut off the rotted section and attach a new timber wall plate to the existing with an angle and through bolt it?

For the timber rafters, would you nail/bolt a timber section (same as the rotted) to the existing rotted section and connect the new section to the wall plate using skew nails?

The loads that we are dealing with here are quite low. Only roof loads, no snow load but there is wind load from hurricanes. Although the local code doesn't normally need tie-downs if the roof is fully slate, which it is.

Any help with sketches or guidance would be appreciated.

Thanks!

 

[BAretired]

The roof should be nominally tied down, notwithstanding the slate. I find it difficult to understand the purpose of all of the wood members. I have numbered them below and wonder if you could indicate the purpose of each by your understanding.

BA

 

[dik]

Not good... there could be a lot of remediation. Wood brown rot (aka dryrot) can lose 20% of it's strength without any noticeable, weight loss. The damage you show is excessive. The fungi attacks the cellulose in wood fibre, leaving the darker lignin materials behind. Hence it's name brown rot. It may be possible to reconstitute the wood members using penetrating epoxy. This may be available at marinas... it's used to repair boats with rot conditions.

First thing to do is to find the source of the moisture and eliminate it and the source. Brown rot contrary to the name dry requires moisture... generally in excess of 22%. Other sites say higher, but if my moisture meter reads in excess of 22%, I think brown rot is possibly an issue. The fungus spreads by sending out little 'water tubes' called hyphae that take moisture from wet areas and draw it to new areas to deteriorate. I've attached a paper on brown rot for added info.

Good Luck... you have a difficult task at hand.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[BAretired]

Dry rot is not simply a structural issue. It is also a health issue, which means that the contaminated material should be removed. See the link below.

https://www.bsv.ca/home-mold/dry-rot.html

[/url]

BA

 

[Redacted]

Hi there,

Sorry for the confusing image. I have attached an image that is zoomed out to provide a better view.

Item 1. Timber wall plate that is sitting on top of the masonry wall and lintels.

Item 2. Rafter for a pitched roof.

Items 3, 4 and 5. Seems like a previous designer/contractors way of having the foyer slate bear onto the rafters.

The ends of the rafters have started to rot due to water ingress. The water leak has been patched. Essentially I would like to sister the affected 3 rafters, with the same timber cross section and have this new timber bear onto the wall plate.

New timber sister rafter to be connected to the wall plate with two 20d skew (toe) nails.

The timber is only affected by the water dmg rot at the bottom where it is meant to bear on the wall plate.

Initially I was thinking of sistering another piece of timber up to the collar tie location (50% of the rafter height). What are your thoughts on this?

Also thanks for providing the information on dry rot, very helpful.

I am wondering what the ideal connection would be for the rafter sister connection. E.g. through bolts or nailing arrangement?

 

[BAretired]

The new photo is a much clearer representation of the existing construction. It would be desirable to remove the affected material completely, but I'm not sure that is possible.

It would be prudent to investigate the removal of the health hazard by disinfecting all of the contaminated material, which are all in a fairly confined region.

I like the idea of sistering a member half way up the rafter height. The new members should be either preserved wood or steel, one each side of each affected rafter and through bolted.




BA

 

[dik]

Give my paper a read...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Redacted]

Thanks BAretired For clarity you mean like the attached detail correct? Unfortunately removing the entire rafter would require significant roof works, which the client is not willing to do.

Yes, I will follow the proper health and safety precautions when removing the affected section.

Dik, your article is insightful. Thanks.

 

[dik]

The paper was put together for structural reasons... but addresses health issues. As BART noted health issues can be serious and life threatening. I didn't mean to detract from his health related comments. They used to use a bleach and detergent mix for cleaning and the current practice is to use detergent only... I understand this is because some of the products of oxidation for some 'critters' can be toxic.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dik]

Like it or not... the client may have to do this and may not have a choice... from the appearance, you are likely down to less than 10% of the material capacity. Clean it and epoxy treat it ASAP. I have photos of some projects where I was able to push the full length of my Swiss Army Knife blade up to the handle... Without penetrating epoxy treatment, the material may not be strong enough to 'sister to'.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Ron]

@dik...thanks for the paper. Good one.

Wood rot is fungal. If left in place, can attack your sistered members as well, though not common to do so if the water source is removed.

This is a common problem in my area. We usually handle by sistering, sometimes by splicing and sistering.

 

[dik]

BART's link has some good information, too...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[BAretired]

RStars:

Your sketch shows only one bolt. If there is any moment in the rafter, you need a minimum of two bolts for stability. The bolts must be sufficiently far apart to resist the moment, but the lower bolt cannot encroach on the rotten material. See below.

BA

 

[XR250]

Can we all agree to call "Roof Rafters" just "Rafters". It is redundant. Pet peeve of mine.