Expecting Dad Planning Addition to Family Duplex in California

[Duplo]

Hi All,

I'm researching to determine feasibility for an 865 sq ft addition to a 765 sq ft unit of an existing 2,448 sq ft duplex that was built in between 1946-1956. This addition will bring this unit to roughly the same size as the other unit but also attaching the existing duplex to the existing 410 sq ft garage increasing the total building size to 3,738.

The municipality adopts the 2022 California residential building code (which I believe governs duplexes) and does not modify it in ways that concern me. However I'm not exactly clear on what portions (if not the entire building) of this project they are going to determine is new construction and hold to current building codes.

The building permit application states requiring the following:
B. DRAINAGE / GRADING PLAN / SOILS REPORT / TITLE 24 AND OTHER CALCULATIONS A drainage, grading plan and soils report is required for any second-story addition or any addition over 700 sq.ft. At least 2 copies of the required reports and calculations shall be provided. Engineering and energy reports may also be required.

The project will also alter portions of the existing 765 unit by opening a portion of the exterior wall to create an addition for an additional kitchen area, hallway, 2 bedrooms, 2 bathrooms, and door to backyard. As well as replacing and adding plumbing, electrical,

I attached a roughly sketched and scaled floor plan:
Green lines to show the existing duplex building areas, walls, and garage that I am not structurally altering
Red is the area of the addition
Blue is an interior wall I am planning to move a 2 feet over (living room area is a little small so every inch would help).



I'm assuming that this is not an easy question for anyone to answer with the details I've given. I'm trying to get as far as I can before I have to start paying out thousands of dollars to the engineer/architect and plan checkers, especially if I can determine this just isn't feasible. I'm trying to read through the building code to understand what I can expect to have to do to get this permitted/determine feasibility. Any and all comments or references to relatable codes would really help me!

 

[TheCommish]

From the east coast good luck

 

[bill1952]

There are things I might see if I could walk the site, but looks ok from just seeing the drawings. I did wonder if the the existing detached garage had a foundation suitable for it becoming attached and becoming load bearing walls for the addition. I can't think of other things that might be a really big deal. Any storm drains or other underground utilities in the area of the addition; utility lines overhead, could be costlier to overcome.

Good luck!

 

[Duplo]

There are things I might see if I could walk the site, but looks ok from just seeing the drawings. I did wonder if the the existing detached garage had a foundation suitable for it becoming attached and becoming load bearing walls for the addition. I can't think of other things that might be a really big deal. Any storm drains or other underground utilities in the area of the addition; utility lines overhead, could be costlier to overcome.

Good luck!

Thank you, yes I am working to get a design/builder out to walk it with me and review my plan but time is $ for a lot of builders who are extremely busy out in my area. And I hate spinning people's wheels without doing my own homework as much as possible and I also think its important that I am somewhat able to confirm what they are telling me and understand what they are saying. I am paying a licensed civil engineer a minimal fee to come out to meet me today onsite and review my plan and perform an inspection of the structural elements of the existing buildings. I am also getting a bid for a geological/soil study and a surveyor to confirm the precise the precise boundary lines.

In regards to feasibility, I'm really trying to minimize disturbance to occupancy of the other unit with this addition and alteration (my family lives in that unit now and will need to live in for a majority of the project and after). I'm trying to limit the scope of work as much as possible to minimize costs. I'd rather defer work on the other unit for as long as is responsible and we have the budget to do it. I have updated the plan to illustrate the additional detail I am providing below.

The garage is built on a 20x20 concrete monolithic slab with pretty thin walls - I'm assuming I'll have to lose square footage in the house to increase the thickness of the wall to accommodate insulation and fire rating where it attaches which would probably require me to changed my proposed addition footprint and add a little bldg square footage to my plan to keep the spaces sized as they are.

The existing building is on a crawlspace foundation (not sure if its bolted on). It has concrete stemwalls - not sure if they have rebar in them since I understand that may have not been a practice in the 1940s but this house could have possible been built in 1951 or later in the 50s. Maybe I should take a metal detector to them if it matters?

There are no overhead utility lines in the area of scope, they enter our property on the east side of the building opposite the garage side, do not run in front of the property, and enter the neighboring property from the south side, both over 50ft from scope of the addition. Water enters from the front but runs to the other unit first then t's off. There is plumbing for 2 meters but foolishly somebody decided to remove the 2nd meter and reduce to one meter awhile ago so we'd have to go through getting the 2nd meter back. We do have two existing electrical meters.

The existing detached garage and duplex roof is a tear-off replacement now due to its condition. We plan to replace the existing duplex front windows & exterior siding, extending/adding to the shared front porch concrete slab and extending a portion of the porch overhang to accommodate moving the existing front door of the addition unit with the addition closer to the street on the same wall to get more living room area. Municipality requires a building permit to do all of this so I'm figuring to do it all under one permit if possible at the same time to reduce costs with economy of scale.

 

[bill1952]

An attached garage on a slab would not fly hear because of frost and replacing the foundation for it would make it a tear down. Could be all different on your climate.

 

[Duplo]

attached garage on a slab would not fly hear because of frost and replacing the foundation for it would make it a tear down. Could be all diff

Ah, well the location is Southern California coastal city... mean annual temperature is 61 degrees. Not sure how much discretion the building department has regarding frost protection for foundational requirements. You mean possibly needing to tear down and rebuilding the garage?

 

[bill1952]

I would have to. I suppose I could lift it and excavate and put in a frost protected foundation and lower garage onto new foundation. Just have to see if that made sense.

No idea of what you'd be required to do but California does not seem lax or prone to use much discretion in these matters. You could be fine.

 

[Duplo]

I would have to. I suppose I could lift it and excavate and put in a frost protected foundation and lower garage onto new foundation. Just have to see if that made sense.

No idea of what you'd be required to do but California does not seem lax or prone to use much discretion in these matters. You could be fine.

The structural engineer I had looking at my plans and the duplex today recommended doing a sister foundation and wall along the outside of the garage instead of structurally attaching. And then doing a California roof that is not structurally supported by the garage, just lies on top. Do you think that would fly?

 

[bill1952]

Local call but the separate foundation and walls would seem to be very close.

 

[MtnArch]

The structural engineer I had looking at my plans and the duplex today recommended doing a sister foundation and wall along the outside of the garage instead of structurally attaching. And then doing a California roof that is not structurally supported by the garage, just lies on top. Do you think that would fly?View attachment 13089

Frost protection in California is generally 12" only (though in the Sierra's it may deepen). Generally the engineer's recommendations are close to what I'd recommend; however, if you're going to go to the trouble of pouring an additional footing and framing new walls around (outside) of the garage you might as well just demo the garage and build it new. Depending on how close to the side setback you are at the back corner of the garage you may not be able to do that anyway.

What you're proposing is fairly standard in most of California and - especially in your area - should go fairly smoothly.

You might speak with the AHJ about the soils report. The AHJ has the ability to waive that if they have prior experience/data from the area with the soil, and usually if it's in an established neighborhood they will accept using code minimum values.

 

[Yikes]

Duplo, welcome to the forum. Trying to understand the goal of your first post: is your goal to avoid getting a geotechnical report?

Assuming your location “93013” is your zip code = Carpenteria: it is understandable that this coastal community is asking for a geotech report, given history in other nearby areas of stormwater, mudslides etc., even though your house may not be near those problem areas.
Note that the cost of a geotech report may be partially or wholly offset in savings on it giving you design factors that will allow for smaller footings than what the code prescriptively requires when no report is available.

Have you gone to your local building department to see if any of your neighbors had obtained a geotech report for their own projects in recent years? You may find one close enough to either use for initial design and budget, and/or contact that report provider and see if you can get a report modified for your house.

 

[ICE]

Somebody is proud of the framing:

Garage to House roof join (aka California Fill) by Preciado Wood Works

Had to frame out a "California Fill", to join the roof of the garage to the main house. This roof had rot in the garage joists, so had to remove the joists that were rotted, replace the joists and make a new fill area to sheet over.

www.preciadowoodworks.com

 

[ICE]

Have you gone to your local building department to see if any of your neighbors had obtained a geotech report for their own projects in recent years? You may find one close enough to either use for initial design and budget, and/or contact that report provider and see if you can get a report modified for your house.

A community that small probably has a good idea what the soil type is. Many jurisdictions allow you to go with expansive soil and call it a day. That results in 12"x 24" footings. Asking for a soils report for a nearby property will not get you anywhere. The soils engineer has a mortgage to pay so you can forget about changing the address on an existing report.

You mentioned hiring a surveyor. In a neighborhood from the '50s I would expect there to be indications of where the property lines are. Looking at the drawing that you provided is appears that there isn't a need for a surveyor to infill between a house and a garage. A slightly more expansive site plan could provide definitive proof of that.

 

[Duplo]

Duplo, welcome to the forum. Trying to understand the goal of your first post: is your goal to avoid getting a geotechnical report?

Assuming your location “93013” is your zip code = Carpenteria: it is understandable that this coastal community is asking for a geotech report, given history in other nearby areas of stormwater, mudslides etc., even though your house may not be near those problem areas.
Note that the cost of a geotech report may be partially or wholly offset in savings on it giving you design factors that will allow for smaller footings than what the code prescriptively requires when no report is available.

Have you gone to your local building department to see if any of your neighbors had obtained a geotech report for their own projects in recent years? You may find one close enough to either use for initial design and budget, and/or contact that report provider and see if you can get a report modified for your house.

Please see my revised floorplan design, green lines to note existing walls, all other walls would be additional interior or exterior walls.

Plainly, I'm just trying to learn what can of worms I may or may not be opening with this project and what the most cost effective, yet prudent, final scope would entail. (Such as having to budget to replace the garage which would include removing everything that's in the garage and disabling it's use for the duration of the construction OR alternatively planning for a sister wall if that's actually feasible). Considering I need to financial plan now for the future. My philosophy in regards to planning is to ask all the questions to identify and assess all of the risks before committing. Being inexperienced, I'm just trying to figure out what questions I need to ask and issues I would need to explore. I appreciate any feedback/help so any and all comments are appreciated.

I'm not trying to achieve getting around anything that I'm required to do and I especially want to consider pros and cons as I do want to preserve this building for as long as possible as it is very important to my family. Nor do I think there are actual problems with the existing building, zoning, and setbacks. The property is not located in the City's map of problematic soils areas or natural hazards. The structural engineer I had out to inspect gave me a verbal opinion that he thought I probably had absolutely no issues with the soils considering the existing concrete stem walls for the duplex have existed for 70-80 years and have appeared not to budge an inch. I do have neighbors who have performed drastic renovations/rebuilds and I do not believe they had issues with the soils.

The engineer also said that the unit I am considering an addition to was built like an addition to the other unit with independent structural components and I could tear down the existing unit I'm looking at adding onto to the dirt and rebuild it if I wanted to.

What I am trying to do is plan ahead and figure out what a plan checker and inspector is going to be looking at in my design of the addition. And how to best design it so there are no oversights so I can try to eliminate unforeseen costs as much as possible before committing to the project. And I also am trying to evaluate if it makes sense to just tear down the unit and garage and rebuild - but I think that would increase the project cost quite substantially as opposed to doing just an addition and alterations to the existing unit.

 

[Duplo]

A community that small probably has a good idea what the soil type is. Many jurisdictions allow you to go with expansive soil and call it a day. That results in 12"x 24" footings. Asking for a soils report for a nearby property will not get you anywhere. The soils engineer has a mortgage to pay so you can forget about changing the address on an existing report.

You mentioned hiring a surveyor. In a neighborhood from the '50s I would expect there to be indications of where the property lines are. Looking at the drawing that you provided is appears that there isn't a need for a surveyor to infill between a house and a garage. A slightly more expansive site plan could provide definitive proof of that.

Good points!

Unfortunately the zoning for this property requires planning commission approval for an addition of this scope therefore I do need the survey to provide the elements of a sufficient plot map for the planning commission. I will also likely have to plan to meet or request a modification of parking requirements which may require knowledge of the precise locations of the boundaries and setbacks.

A principal planner of the city advised that I should plan for the addition of at least one covered parking space to avoid uncertainty of not being granted the requested modification. I'm thinking at a minimum they are going to ask me to put in at least one additional uncovered space.

 

[ICE]

A principal planner of the city advised that I should plan for the addition of at least one covered parking space to avoid uncertainty of not being granted the requested modification.

Convert the garage to an ADU and the covered parking requirement might go away. Depending on the proximity to c transportation, there might be no parking requirement at all.