• Christina Blanchard

Building our Foundation 1: Planning & Marking a Grid

The first post in our "Building a Foundation" series, how we planned and marked the grid for our foundation.

With our plan in place and materials procured it was time to get to work on our foundation. The land that the cabin would be built on was cleared and relatively level ( still a slope on the land, but no major rocks or dips that would be in the way).

Laying our Foundation was a HUGE undertaking, so I've broken the process into several posts. This is the 1st post and it covers the 1st step, planning and marking a grid for the locations of the cement pads.

Our Cement Pad Grid for Foundation Supports

Just to review here is the plan for our foundation:

  • Cement Pads placed in a grid each pad will be ~18"wide x 18"long.

  • Cinder blocks, pressure treated lumber, and similar recycled materials (aka stacking materials) will be stacked on each of the pads. The stacking material will be stacked to reach the same vertical height.

  • Stringer/ Beam Spanning across the cement pads/stacks. The stringers are the main support for the cabin and will need to be perfectly level.

  • Floor Joists Spanning across the stringers (perpendicular to the stringers). The floor of the cabin will be nailed directly onto the floor joists.

The first step we needed to complete was to lay out a grid and find the exact locations for each cement pad. This step is essential as the location of the cement pads is also the location of support for your main beams (or stringers) which support the entire cabin.

The steps we followed to layout our grid and mark locations are as follows:

  1. Determine the Spacing of our Foundation Stringers and Floor Joists

  2. Determining the Number and Location of Cement Pads Required

  3. Mark the 4 Corners of the Cabin Ensure they are Perfectly Square

  4. Using Survey Pegs and String, Mark a Grid

  5. Use the Grid to Mark the Location of each Cement Pad

Determine the Spacing of our Foundation Stringers and Floor Joists

The cement pads must be:

  • Spaced close enough that the stringers don't span too far of a distance (spacing in the direction of the beam/stringer). This spacing is determined by the type of beam you are using.

  • Spaced close enough that the floor joists don't span too far of a distance (spacing perpendicular to the direction of the beam/stringer). This spacing is determined by the type of floor joist you are using.

  • Positioned in a grid that is perfectly square, so the beams are parallel, and your cabin footprint is square

Our cabin design has a rectangular footprint of 46' x 26' (see my Cabin Design Post).

For our stringers we decided to use 2" x 10" lumber, laminated together to make 4" x 10" beams, 26' in length. According to carpentry tables this type of beam is good to span 8' to 10' (but this will depend on the type of wood). From this we determined that for the 26' width of the cabin, we would require 4 supports for each stringer.

  • Note on the direction of stringers: Typically the stringers will run along the length of the cabin (for example the 46' long direction). However, based on the cost and the slope of the ground we decided to run our stringers along the width (the 26' long direction). This means we require a larger number of stringers, but they are shorter in length.

For our floor joists we decided to use 2'x 6' lumber from a local sawmill. To determine the maximum spanning distance for your joists you need to know the wood type, wood dimensions, and also the parallel spacing of the joists. Once you have all 3 you can use spanning tables available online or in carpentry books.

  • Note: Typical parallel spacing of floor joists is either 12",16", or 24" on-center (OC). This is the measurement from the center of one joist to center of the next parallel floor joist.

We determined with our lumber spaced 16"OC we could span 9'. This span is essentially the maximum distance between our stringers/beams. That means for our 46' long cabin we would require a minimum of 5 stringers, but due to the design of our cabin we went with 7 stringers. Stringers are shown in blue in the diagram below (running vertically).

Grey boxes represent the cement pad location, 7 blue lines the stringers, green lines the joists

The drawing above shows the spacing of our stringers(blue/ vertical) and joists(green/horizontal). On both ends of the cabin there are rooms 14' wide, with a stringer running through the middle, these stringers are 7' apart. The middle room is 18' wide, with a stringer in the middle, for a 9' span.

Determining the Number and Location of Cement Pads Required

For each 26' stringer (shown in blue) we required 4 evenly spaced supports along the length, therefor the cement pads would be located 8.6' apart.

  • Note: To determine spacing divide the length of your stringer by the number of spans- NOT the number of supports. For example 26'/3 spans = 8.6' span length

So our 26'x 46' grid requires 4 pads/stringer x 7 stringers= 35 cement pads, spacing shown above.

Mark the 4 Corners of the Cabin & Ensure they are Perfectly Square

Now that we know the spacing of cement pads required we need to mark their locations on the ground. We were working with a very limited space, with a steep slope on the front of our pad and a large rock/cliff behind it. The first thing we did was pick the limiting corner, basically the farthest back we could go on our pad of land.

Once we found our limiting corner, we placed a survey peg (or wooden stake) in the ground. All measurements should be taken from this corner, called the datum. We used a long measuring tape to measure out 26' to the front of our cabin, then we measured 46' across the front of the land to get a general idea of the front of the cabin.

Mike using the measuring tape to measure the front of our cabin (46' side)

Unfortunately, the front corner of the cabin landed on the rocky, steep slope (shown in the picture above). To fix this we knew we would have to change the angle of the cabin in relation to the datum corner. We remeasured 26' and 46', changing our angles, until we had all 4 corners on our leveled land. We drove a stake in the ground to mark the approximate location of corner # 2 (the corner measured 26' from the datum). Next we needed to find the exact locations.

It is important that the corners are perfectly positioned, otherwise we would be dealing with a non-square foundation and a non-square cabin. That would be a building nightmare. This is the part where I got to bust out some of my nerdy engineer knowledge... aka the Pythagorean Theorem!

For those of you who are less excited about math, the Pythagorean theorem is actually a super simple calculation that can help you make a right-angle triangle. Right-angle triangle = perfectly squared corners.

The concept is that if you have a right angle triangle, with 2 known-length sides you can calculate the length of the 3rd side! The formula is a2+b2=c2 (2=squared), see the picture below.

The width of the cabin is 26', the length 46', so the measurement corner to corner (c in the above picture) is 52.8'.

Next we ran a line from corner 2 to the approximate location of corner 3, marking on the line 46'. Then we took our measuring tape from corner 1 to corner 3, marking on the tape at 52.8'.

Mike took the 46' line, and I took the marked measuring tape, we brought our lines together until the 46' line intersected with the 52.8' mark. The intersection point of 52.8' on the measuring tape with the 46' mark on the line should be the exact location of corner 3. This will ensure that corner 2 is a right-angle.

Next we repeated the process for corner 4.

Then we re-repeated the process for all 4 corners. I think we may have "double-checked" our corner locations ~10 times. Better safe than sorry.

Using Survey Pegs and String, Mark a Grid

Once we had the exact locations of all corners we drove stakes in the ground and ran 4 lines to make a square. This square is the 26'x 46' outer perimeter.

The picture below shows we ran the lines from separate stakes to ensure the corner marking pegs were not disturbed. In the picture below the stake with the flagging tape marks corner 4. You can also see corner 1 (upper right side of photo) and corner 2 (middle of photo).

Our grid made of surveying string secured with wooden stakes

Use the Grid to Mark the Location of each Cement Pad

Next, we marked along our 46' lines (with duck tape and flagging tape) the location of the stringers. Then we ran 5 additional lines, across the grid, in the location of the stringers. We then remeasured, and made sure the stringers were square/parallel. Next, along each of the lines we marked the location for each of our 35 cement pads.

Once we had the location for the cement pads marked on the string grid, we wanted to mark the locations on the ground (just in case the stakes or strings got knocked over or moved). We tied pieces of neon flagging tape to 4" nails and drove the nails in the ground so that the tape was showing. I did this to mark the location for all 35 cement pads.

There you have it, the foundation is planned out and marked! Time to celebrate with a nice long nap! The foundation build continues next in Building our Foundation 2: Pouring Cement Pads.

Duke enjoying a siesta after a long day working in the summer humidity

Disclaimer: We are not design professionals or carpenters. The purpose of these posts is to share how we did it, but by no means take what you read here as design or construction advise. Always do your own research, talk to professionals, and follow local codes/regulations.

About Christina

I'm Christina and I live in the beautiful Canadian province of Newfoundland & Labrador. We are building a cabin by the ocean in rural Notre Dame Bay. Come along with Mike, Duke and I as we pursue our version of the Islanders dream!

Stay Updated

Subscribe to follow along!

Stay Updated

Follow along with us as we build a cabin by the ocean. Subscribe for a weekly update.

Disclaimer: The information given on this website is for reference and inspiration only. When starting a building project always consult professionals and follow local laws and regulations. 

© 2019 Christina Blanchard. Proudly created with Wix.com