Epoxy Anchor into Stone Foundation Wall 1

[StrucDesignPE]

Architect wants to put a new deck on an old house. Typical deck framing with PT wood ledger attached to foundation wall of the house. The foundation wall is a stone (probably limestone) wall that is +/-18 inches thick. House is about 100 years old. In my short structural engineering career, I haven't had any experience with epoxying anchors into natural stone and to me, it presents some unknowns:

1) None of the manufacturer's of epoxy anchors offer guidelines for using their products in stone. I checked Hilti, Powers, and Simpson. I figure its because of the infinite types of stone that could be used.
2) Edge distances for the stone
3) Embed depth

Any help or suggestions as to how I should tackle this would be very much appreciated.

 

[Archie264]

I'd recommend against it and instead try to make it a free-standing deck as shown in this publication: DCA6-12

Also, there was some recent discussion on residential decks on this forum from just a few days ago that might be of use to you.

 

[XR250]

Wouldn't the deck band be attached to the floor band of the house? Usually some large timber on an old house like that or does the stone continue up past?

 

[StrucDesignPE]

The detail that the architect has provided to me has the stone foundation wall continuing up to just under F.F.E. because the interior floor joists are pocketed into the wall. Therefore, the ledger has to anchor into the wall.

I am going to recommend the free standing option, but don't think they will go for that.

 

[StrucDesignPE]

By the way Archie, thanks for that article. As a young engineer, I am always on the lookout for good resources.

 

[XR250]

You could hold the posts off the house and the edges of the deck a couple of the feet by cantilevering the framing. If the deck is not too tall, the supports tend to disappear.

 

[jeffandmike]

Agree with Archie264. There are several good reasons to make the new deck freestanding. For one, you can't be accused of damaging the existing structure in any fashion if your new structure isn't actually attached to it.

Second, I am assuming that some kind of mortar was used to cement the stone together. Have you checked the condition of the mortar? I've looked at numerous very old stone foundation walls in the northeast and frequently find that the "mortar" has basically turned to sand/dust. Probing it lightly with a screwdriver often results in it flowing out of the joints. How confident are you in what you would be attaching to?

Any holes you place in the wall(s) for your connection end up being potential sources of moisture intrusion (though, I guess this is less likely with an 18 inch thick wall)... not necessarily an issue if it's an unfinished crawlspace, but more likely an issue if it is living space on the other side.

How were you intending to detail to ensure against cross-grain bending of the ledger? Again, not the easiest to do in the situation you've described.

If you truly are at the whim of the architect (as is often the case), and have to connect to the wall, minimize the importance of the connection... the way XR250 described.

 

[StrucDesignPE]

I was able to get the architect open to the idea of a freestanding deck. I agree with XR250's comments about cantilevering the framing and keeping the posts away from the existing foundation wall.

Jeffandmike,
I had the same concerns with the mortar joints. The house is 100 years old and the mortar looked pretty soft. I had initially thought that if I could keep the anchors set in large stones, this might not be an issue. The stone that this wall was built with is relatively flat and irregular in shape so trying to tell the contractor to only anchor in certain stones would have been difficult at least.

I think the freestanding deck is the best way to go and I will just add a few ties to brace the deck laterally.

 

[bridgebuster]

You can anchor into the stone, just call for a pull-out test. I have a project with a contractor where this was recently done. They had to anchor a 70' tall temporary stairway to a bridge pier - just granite blocks. The stairway designer used Hilti Kwik-HUS EZ (KH-EZ) carbon steel screw anchor. Their calculation assumed compressive strength of 2,500 psi. I don't know the results of the tests, other than OK. The anchors were designed fr 1.5 k tension and 1.5 k shear.

 

[SLTA]

The mortar is likely a lime-based mortar instead of cement-based. It definitely tends to turn to sand after exposure to weather over time. WHATEVER YOU DO - please don't let them go back in and tuckpoint with a hard cement-based mortar. It could likely bust apart the stones and the wall.

http://www.nps.gov/tps/how-to-preserve/briefs/2-repoint-mortar-joints.htm

Congrats on the freestanding deck agreement!

Please remember: we're not all guys!

 

[XR250]

@bridgebuster;
I would be worried the stones would pull out of the wall assembly.

 

[RHTPE]

XR250 makes a valid point regarding the stones pulling out of the wall assembly.

I just want to put in my vote for a freestanding deck. After seeing the results of poor owner maintenance of decks constructed with ledger boards and joists perpendicular to the house wall, I am a strong advocate of decks designed as freestanding for gravity loads with appropriate ties to the house for lateral loads (or appropriate bracing for lateral loads). This way there can be an open "slot" between the house and the deck so that debris accumulation does not occur. It is the debris accumulation that leads to moisture damage over time.


Ralph
Structures Consulting
Northeast USA

 

[MacGruber22]

My thoughts:

1. You could scare them away from attaching to the stone with a very heavy-handed testing program. It is always good when the client, arch, or contractor makes a choice on their own, rather than for to ram your opinion down their throat. Use your intellect to coax them into choosing an outcome that satisfies your concerns.
2. If you really decide to anchor somehow, what about diamond core-drilling and grouting in threaded anchors? Personally, I would feel better if I could replace a decent amount of the stone around the anchors with a grout (that may not fly aesthetically, though). Jahn repair mortars are generally regarded as the cream of the crop when it comes to stone, cast stone, and masonry repair. Whether epoxy, grout, etc. you have to have a material that is compatible with the long-term behavior of the connected material. I wouldn't chance it on a typical structural epoxy adhesive.
3. Stainless steel through-bolting and sealing the hole before you set the rod?? You could use some monster stainless washers between the wall
4. Regressing from my number 1 - tell the architect to eat dirt and deal with a separate line of support.

"It is imperative Cunth doesn't get his hands on those codes."

 

[MacGruber22]

Sorry - here is the link to the manufacturer of the Jahn masonry products.

http://www.cathedralstone.com/

"It is imperative Cunth doesn't get his hands on those codes."

 

[MacGruber22]

Or...scare them from wanting no separate exterior support along the wall with this...

"It is imperative Cunth doesn't get his hands on those codes."

 

[RHTPE]

MacGruber22 - I like your sketch - kinda like balancing a teeter-totter on a keg don't you think? Your sketch (great concept BTW!) will certainly discourage the architect if the interior aesthetics matter.

It might be a rather stout column and an interesting footing depending on the lateral loads to accommodate. How the stones were laid will influence the degree of resistance to horizontal movement one should anticipate. Also, I wonder what size rod if the amount of stand-off on the exterior increases (to provide for air flow to 'flush' out most debris).

I still think the ideal way to frame a deck is to have the main beams perpendicular to the house wall.
- Support the main beams on 2 (or more) posts, cantilever each end. Make it a stout beam.
- Joist run parallel to the house wall, 1st joist about 6-8" from the house wall.
- Deck cant's over that joist closing the gap along the house to 1-1.5".
- For lateral stability, tie the ends of the main beams to the hose framing (or foundation) with a connection that allows for settlement/heave of the post footing.
- X-brace the underside of the joists and tie braces to the beam(s) directly over the posts.
The area below the deck is then free of headache causing obstructions.

This (or any other) situation may vary.

JMNTBHO


Ralph
Structures Consulting
Northeast USA

 

[MacGruber22]

Ha! I thought the first response I was going to get was a laugh and/or scolding. Thanks, RHTPE.

Frankly, now that I am looking at my sketch, I would also underpin the existing wall in that area so that you reduce any movement after the fact. Then *maybe* you could get the resultant into the kern of the new footing.

It is certainly giving StrucDesignEIT some ideas to chew on.

"It is imperative Cunth doesn't get his hands on those codes."

 

[StrucDesignPE]

Yes, it certainly has given me some ideas to chew on. I am glad the architect was open to the freestanding deck. I think MacGruber22's concept might have convinced them to go the freestanding deck route if they were hesitant about it. Thankfully *this* architectural firm is easy to work with.

 

[jeffandmike]

Gotta love MacGruber22's detail...

Is that a tube steel member going through the wall? If so, to allow for full transfer of out-of-plane forces into the cantilever column, and not into the stone wall, the tube steel member should be sleeved or greased. Even with this, you still have the cross-grain bending issue on the "ledger"/girder. It would be better to somehow tie the lateral support into the deck joists.

The detail actually looks somewhat legit when you consider the craziness that is sometimes required to address lateral load path constraints on old, existing buildings located in areas with high seismic forces. I've never done anything quite this bad, but I have had to resort to cantilever columns for portions of the primary lateral system on several occasions where space constraints were present.