Primer - Anchoring Framing to Foundation

Hey folks, thanks so much for continuing to visit this blog, even though my activities have been 100% occupied with building theEnclosure.ca and the last article I posted here was all the way back in February. As promised, I intend to post more technical themed articles to this blog and use the project journal on my build site for my day to day thoughts and tribulations on building an energy efficient home.

So, it is time for an article that provides a primer into Anchor Bolts. In the days of old, a concrete placing crew would just embed a 1/2" anchor every 4ft or so and call it a day.


Most dwellings had either small cripple walls placed above the foundation wall or had the floor joist assembly sitting right on top of the sill plate. Both of these were able to easily accommodate the location of the anchor bolt with little effort.


Modern construction has changed a great deal in this regard. In areas of high seismic activity, the location of anchor bolts is critical to meet either the code prescriptive path to seismic rigidity, or an engineered path. For us @ theEnclosure.ca, we were forced by the Municipality to upgrade from the Building Code prescriptive path and instead use the prescriptive path laid out in Canadian Wood Council's Engineering Guide For Wood Frame Construction Part C.


In Part C, the requirements for anchor bolts for my region (Lower Mainland BC, Canada) are laid out as follows:

- There must be two bolts minimum per braced wall (seismic) panel

- The bolts must be installed no more than 1.64 ft from each end of a foundation wall

- Bolts must be installed every 7'10"

- 1/2" embedded 4" into the concrete


It is interesting, in contrast, the BC Building Code required 1/2" anchor bolts spaced no more than 5'6" apart (7'10" was allowed but only for 5/8" bolts).

So now, it is critical that prior to your concrete crew coming, all anchor bolt locations are marked out on the form work to comply with the newer seismic regulations. It is also important that the setback from the foundation wall face is identified to ensure that the anchor bolt will miss objects like rimboards (engineered wood) or rim joists (real wood).


For our construction, we had an added level of difficulty surrounding the placement of these bolts. Our design includes a dropped floor assembly that is flush with outside grade in order to meet the requirements of SAFERHome Society. But code still requires that the foundation project 6" above grade (BCBC 9.15.4.6) which results in a concrete foundation stub projecting above the floor surface.

Building code requires the foundation to extend 6" above grade to prevent wood components from rotting.  On a floor assembly that is flush with grade (dropped), this results in a concrete stub extending above the floor.

As my wall framing was then mounted directly to the foundation, it was critical that in addition to meeting the seismic requirements, I also had to ensure that they were placed to miss my wall stud framing. I was about 85% successful in this endeavour. The rest had to be cut off and replaced with drill-in anchors, which my inspector stated would accept for a limited qty.


SO, you have all your anchor bolts embedded at the right locations, lets add the washer and nut and call it a day - right? From a code perspective, you would be right. But there is a best practice when it comes to anchor bolts. I have to thank one of my Home Inspection client's Nikolas for this information.


Turns out that the washer makes a perfect wedge to split the plate apart during an earthquake as the bolt bends under the shear loads exerted by a quake. Who knew??? I reviewed the article that Nikolas sent and written by Howard Cook titled "The importance of Plate Washers"


Howard retrieved the following graph from the Los Angeles Building and Safety department (a group that knows a little bit about earth quakes don't you think!)

You will see that at every point along the graph, that the wall using a plate washer deflected less for a given force when compared to the round cut washer. By introducing a 3" x 3" plate, you are able to better prevent the bolt from bending under shear and preventing the splitting of the sill plate. The mentioned article includes a sketch by Nels Roselund that shows the reactions involved.

Based on this information, we elected to use the 3"x3" plates on The Enclosure but did run into problems on many of the bolt locations. Unless the anchor bolt was dead centre in the 2x4 sill plate, there was not enough room between the sheathing and the bolt or the inside face of the stud and the bolt, to place the plate. SO we used the plates for as many of the bolts as possible and then just the standard washers for the rest.

Just enough room for plate between bolt and sheathing

This bolt was placed too far outboard to slide the plate on.

Howard has also published an article titled Bolting: Attachment Of The Mudsill To The Foundation for those interested in additional reading. Nikolas also forwarded the article QuakeCheck: When the big one comes, will your home be "Safe enough to stay?" which made for a great read to further brush up on this subject and how to address it.


If you have an older home, it may be time to upgrade your anchorage. Is it not worth a few hundred dollars and one day of your weekend to make your family as safe as possible in a seismic event?


Thanks for visiting!

Death of Part 9 construction?

Never would I have guessed that the Building Permit process would be the biggest stumbling block in building your own house.  I know the building code quite well and had ensured my design complied with it.  What I did not allow for, and what may shut me down, is bureaucracy.

It seems that there is a general movement in Municipal building departments across the Lower Mainland to 'opt-out' of Part 9 construction now that this part of the code includes 9.23.13 Bracing to Resist Lateral Loads Due to Wind and Earthquake.  Whether the motivation of the Municipalities is based on fear (many may not be adequately trained on the new requirements that were enacted just last December), or from a perceived workload concern - I am not sure.  It may also be an unjustified fear of liability perceived present if they are responsible for ensuring a dwelling meets the new Part 9 requirements.

Whatever the motivation, the outcome may very well be the death of Part 9 construction in parts of BC and the significant increase in construction costs as a result.  With the added costs of an 'engineered' approach to the Lateral Load design expected to be somewhere in the $20K - $30K range )most of this would be for the added Simpson hardware utilized in most engineered designs), this 'component' has gone from $0 to one of the most expensive components within the home, on par with a high end window, cladding, or HVAC package.

For me, the removal of my ability to generally design and build my own house is similar I am sure to how some Americans would feel if your tried to take away their guns.  I have always felt it is my right to design and build my own house via the prescriptive path of Part 9 in the BC Building Code.

Yesterday, I was informed that this right is being taken from me.  The DNV building department manager has informed me that my architecture is 'complex' and as a result, they will require that the entire structure is engineered including the lateral bracing requirements.

"We consider your proposal combining part 9 prescriptive design with part 4 structural components inadequate in providing lateral support against high wind and seismic forces.

We consider this as a complex design and as such we, the Authority having jurisdiction, decided not to accept the design path and therefore require you to have a Structural Engineer design and provide signed, sealed drawings for the entire structure."

Many of you will be saying, we have combined Part 9 and Part 4 design for decades and you would be right.  In November of 2013 it would be very common to have a primarily Part 9 designed dwelling that also included manufactured components designed to Part 4.  These components would include manufactured floor joists, beams, and roof trusses.  

What changed?  Well the building code introduced lateral bracing requirements in high wind and seismic zones.  This includes the Lower Mainland of BC and the Southern Vancouver Island region.  The requirement became effective in Dec 2013 and right away a controversy developed.  APEGBC in their infinite wisdom decided that the Part 9 lateral bracing prescriptive design was inadequate to resist high wind and seismic loads.  Now of course we have decades of experience showing otherwise, but they have drawn their line in the sand and refuse to budge.

So while engineers are allowed to design to the rest of Part 9, they are specifically not allowed to use 9.23.13  and must instead design the lateral loading using the Canadian Wood Council guidelines or utilizing a 100% engineered approach (Part 4). And the problem with these approaches (granted based on my limited exposure) is that it is a LOT more expensive to build in this manner as it usually includes significant volumes of manufactured Simpson Strong-Tie hardware.  On a house under construction that I often visit, I was quoted a cost of $16K for just the anchor bolts.

Whether this controversy has influenced the building departments, I do not know, but based  on comments made by the DNV manager, many Lower Mainland building departments are getting out of the Part 9 business.  

Personally I question if this is an abuse of the Municipalities power over the code implementation and feel the need for Victoria to step in and mandate Municipal support for Part 9 design and also introduce a detailed frame work that identifies the conditions that must be present in a design before the AHJ can deem that design as 'complex'.  In short, I believe it is time for a major overhaul in how the Building Code is implemented across the Province to ensure a consistent and fair application across AHJ.

In the meantime, I urge you to specifically ask your Municipality what there requirements are going to be while you are still early in the design.  I was notified of my Municipality's unwritten policy after the design was complete during my building permit application meeting.