Hill House

While we’ve been working away on the Hill House, we also produced the Twigg Residence.  This project is in for permitting and scheduled to break ground soon as well.  Not only is the timing similar, but Twigg is located near the Hill House as well.  Twigg also incorporates some of the same energy efficient features such as: staggered stud wall framing, flash and batt insulation techniques, Warmboard hydronic radiant heat, HRV for fresh air, rainscreen siding and thoughtful use of low maintenance / environmentally preferred products.  Mechanical heating and cooling is provided by an extremely efficient reverse chiller.  The site constraints for Twigg were not as tight as Hill House which allowed us to orient and shape the house to take advantage as much as possible of passive heating / cooling / ventilating strategies.  Another exciting feature, Twigg received grant funding from the city for an eco-roof as well.

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This morning I took a quick inventory financially on exactly what we’re doing.  I’ve had a few people request to see some actual numbers on what a house like this costs.  Due to the nature of trade discounts and resourceful shopping, I feel it would be a bit of a disservice to share information that isn’t true to a real world setting.  Having said that, I will share our time investment so far and explain a little as to what this time is spent doing.

After a very quick initial design study, we had a couple of foundation / excavation subs give us preliminary pricing.  Everyone was somewhere in the $250k – $300k range just for excavation and TEMPORARY shoring…these numbers did not include the actual foundation.  As this number was far above our budget, we have been working back and forth with the structural engineer, geotechnical engineer and excavation sub to do a detailed analysis of the most cost effective direction.  While the cheapest solution is still over our budget, the solution is 23 solder piles driven into the hill at about 5′ on center with wood cribbing spanning between them.  This allows the excavator to make steep cuts, starting at the top of the site and installing cribbing as he works his way down.  after the cuts are complete, anchors get driven into the hill, then the temporary cribbing gets sprayed with concrete – which becomes the permanent retaining wall.  We don’t know exactly where the cost will end up yet, but it will be somewhere between $100k-$200k.

To date, we’ve paid approximately $16k in structural engineering fees (our original contract was much less) and approximately $3k in geotechnical engineering fees (our original contract was around $1,500).  I won’t disclose the fee I’ve paid my office to perform work, but I will say we’re in at about 460 total hours.  The time has been spent on design, going through land use review to increase the height by about 10′, and getting the drawing set about 10% through CD’s (detailed floor plans, detailed roof plan, detailed site plan, preliminary sections, preliminary elevations, preliminary electrical plans – no interior elevations yet).  I’d estimate before we submit for permit, we should be in the 500 hour range.  I know there are several ways to structure an agreement with an architect, but regardless, it all comes down to the time spent…even if they quote you a percentage of construction cost – it’s still ultimately about the time spent.

After an exhausting exploration of foundation options (thanks for the work Mike, Craig, Jorge and Manual), we have concluded that for our specific site conditions, cantilevered soldier piles will be the most cost effective approach.  Not cheap by any means, just the most cost effective option we have.  I’ll post a drawing when we have one, but at present it looks like we’ll have about 22 steel piles that are cantilevering out of the ground between 5′ and 20′ depending on their location.

We’ve hit a bit of a sticking point at the moment.  Our structural engineering is basically 90% complete, but we’re now faced with a few options for one very important retaining wall.  We have an option of designing an almost impossible 17′ cantilevered retaining wall that is 24″ thick with #6 rebar placed at 3″ o.c., or using solder piles for a wall up the hill to eliminate the surcharge the upper walls are putting on this lower wall.  For those that don’t know, #6 rebar at 3″ o.c. =  insane!  As always, Wikipedia has a great explanation of a solder pile.

It all gets very complicated, and frankly it’s a little beyond my skill set.  Luckily we have a great team (excavator/foundation sub, structural engineer and geotechnical engineer) who are all working together to get to the bottom of this.  We should have a few estimates by tomorrow that will help me make an informed decision on type of structural system so we can get this thing wrapped up.

i thought i’d post another image precedence showing the movement of the form of the house.  not the most exciting post, but it’s friday and you do what you can.

until i figure out how to post an image or two on this front page using html, i have posted a couple of 3d image of the house in the ‘rendering’ page listed below on the blog…more images, drawings and sketches to follow…

i’ve started this post to document our adventure designing and building a conceptually progressive house on a very difficult site.  stay tuned for more…