# Roof rafters, floor joists. Wood to mortar contact.



## Baltimore (Mar 16, 2012)

This probably could have been posted in the carpentry forum just as well.

A local building inspector recommended installing new rafters with their ends wrapped in 30# felt paper as a wise upgrade from Code. The idea to keep untreated wood separated from the brick mortar found in the walls that they are secured to because, so the thinking goes, the portland cement in the mortar mix will breakdown the wood in the long run. I've seen a good number of 100-150 year old homes (with true 2x rafters) having rafters showing no signs of decay. What am I missing here? I get that wood should not have ground contact, as say might often be found in basements, concrete basements, outdoors, etc. but why am I not seeing the decay that I would would have expected?

Assuming that separation is wise, does anyone have any separation suggestions apart from 30#?

Many thanks.


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## stuart45 (Oct 7, 2009)

I've never heard of OPC causing wood rot. The ends of joists are wrapped if put into the older solid brick walls where they could be in contact with damp brickwork.
However the timber roof plates are bedded on the inner block walls with OPC mortar. The main issue is dampness.


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## fjn (Aug 17, 2011)

*wood rot*

I agree with Stuart45,never heard of opc causing a problem with wood. As stated, to wrap the ends of wood placed in brick pockets is good practice,it prevents wicking of moisture. I would prefer a peal and stick membrane as in Grace Ice & Water Shield,it would provide a better seal at laps. Another method used in heavy timbers was the Goetz-Mitchell anchor,it provided an air space to prevent rot,and apositive connection to help create the building diaphram along with a way for the member to "drop" out of the wall in a fire event without turning the wall over. see item 226


http://chestofbooks.com/architecture/Building-Construction-V2/Slow-Burning-Construction-Part-2.html


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## JD3lta (Nov 22, 2009)

^^Always used ice and water shield for separation.. Unless for expansion and that's classified.


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## dom-mas (Nov 26, 2011)

fjn said:


> along with a way for the member to "drop" out of the wall in a fire event without turning the wall over. see item 226
> 
> 
> http://chestofbooks.com/architecture/Building-Construction-V2/Slow-Burning-Construction-Part-2.html


They used to cut the ends of beams and joists at an angle in old mills around here for the same purpose.

And i agree with the others who say that the portland doesn't cause rot, the wicking does. Lime is actually antibacterial and when used as whitewash is a wood preservative. (not sure if portalnd has the same properties)


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## JBM (Mar 31, 2011)

Good building practice. Ive even used some lead if I didnt have anything else handy for a beam.


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## dom-mas (Nov 26, 2011)

really??? You had sheet lead hand but no blueskin??? Can't buy lead here anywhere. I was supposed to supply lead cpoated copper chimney caps for a contract on a bunch of chimneys. Ended up having to use zinc coated 'cause no one would supply the lead coated


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## JBM (Mar 31, 2011)

Ya there are hundreds and thousands of 50 pound rolls of 8,10,12 inch lead even at lowes and home depot lol. How else would you flash a chimney? Copper !


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## fjn (Aug 17, 2011)

*Lead*

With lead coated copper


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## ohiohomedoctor (Dec 26, 2010)

fjn said:


> With lead coated copper


How would that work at the scrap yard?


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## fjn (Aug 17, 2011)

*Lead*

Lead melts at 850Deg f. you could melt it off and give the junkman a choice,do you want to buy the lead,copper or both?


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## ohiohomedoctor (Dec 26, 2010)

fjn said:


> Lead melts at 850Deg f. you could melt it off and give the junkman a choice,do you want to buy the lead,copper or both?


Thanks, good to know


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## superseal (Feb 4, 2009)

That angle is the fire-cut - mandatory when your bearing on solid masonry. Don't wanna push out the exterior walls on the firefighters during collapse and cause additional damage to the structure.

Just for the record,...I live in a 2 wythe home of 4" block and 4" clay brick and when I remodeled the bathroom, I had about 12 floor joists which I doubled and cut in next to the original pocketed ones. All were in perfect condition with no protection. They didn't forget to fire-cut though :whistling


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## fjn (Aug 17, 2011)

*Floor joists*

In the days that solid masonry bearing walls were prevelent, a fire cut was required on joist ends since 1860.The fire cut was approx.a 30degree cut starting at top of joist just at inner face of wall. To also add stability to the building anchor bolts/rods went from bottom edge of joist to exterior face of wall. On strictly utilitarian buildings a steel pin went through an eye on the end to prevent withdrawl. On "fancy" buildings the end was provided with a decorative cast medallion. The Goetz-Mitchell anchor addressed these needs,while the aforementioned system was used on light framing. For those interested scroll through the link provided.

http://www.gobrick.com/Portals/25/docs/Technical Notes/TN44.pdf


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## dom-mas (Nov 26, 2011)

JBM said:


> Ya there are hundreds and thousands of 50 pound rolls of 8,10,12 inch lead even at lowes and home depot lol. How else would you flash a chimney? Copper !



galvanised step flashing, then painted steel? At least i guess that's what I get. i just ask for step flashing, then go to the sheet metal place and give them the dimensions and they supply me with the finished flashing in my colour choice. whatever i get, I know it's not lead


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## fjn (Aug 17, 2011)

*Flashing*

While we are talking flashing material,one material that is a big nono is aluminum. Mortar contact with aluminum is the kiss of death for it.Mortar will start to attack aluminum before the scaffolding is on the truck.


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## dom-mas (Nov 26, 2011)

fjn said:


> While we are talking flashing material,one material that is a big nono is aluminum. Mortar contact with aluminum is the kiss of death for it.Mortar will start to attack aluminum before the scaffolding is on the truck.


unless it's painted I believe, all 4 sides of course. i think we've all seen the immediate damage mortar can do to aluminum thresholds


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