|How big is a square foot?
By Robert Knight
[Full text of article, an edited version of which appeared in Fine HomeBuilding]
In trying to systematize our price data it became apparent I needed to have a systematic way to compare buildings with different components in order to get a universal kind of square footage.
Generally, people selling houses want them to seem big so the 25X40 sq. ft. screen porch might well be counted as 1000 sq.ft.of living space in the Realtors description. On the other hand when someone has been told that it costs "$100/sq.ft. to build a house" they want the number of square feet to be as small as possible so the estimated cost is less--and then they multiply only by the interior "heated" sq.ft and get that screen porch for free.
|calculations, so adding 20% for a real attic (which is probably more than it costs) tends to compensate for throwing away that square footage. Multiplier =0.20.
Insulated Garage: We think is about 40% of the cost of heated house space. They usually have a good deal of mechanical stuff in them, good windows, expensive doors, a shop work bench, maybe a stair up to a second floor "attic", but they are inherently simple spaces.
Multiplier = 0.40.
Uninsulated or "Raw" garage: We usually use 30%. Because there is less of the above reasons. Multiplier =0.30.
Covered decks, screen porches, and roof decks over inhabited spaces we take at 40% because they involve lots of expensive finishes and detailing. Multiplier =0.40.
Open wood decks we figure at 20%. We find a deck with PT framing and WRC surface, some stairs, railings, some built in seating goes currently for around $20/sq.ft. which is about 20% of heated space at $100 sq.ft. But, you think, what if the house is a luxury model at $200 a foot, the deck wont increase to $40 sq.ft. Wont it? Wont it in fact be a granite patio or be made out of South American Ipe on that level of house? If it truly wont then reduce the multiplier--but dont say I didnt warn you.
The point of this is that the multipliers should reflect the kinds of buildings that you build so that the "Factored sq.ft. number" that you come up with for your buildings will allow you to compare dissimilar buildings.
When we develop a square foot sheet for a house that is at all atypical we often times will adjust the multipliers to be what we feel is a more accurate reflection of this particular building--but they rarely change more than .10 up or down. The important thing is to go through the exercise, and to realize this is only a first look at a building--before you really have enough information to truly cost it out.
Our clients often want to massage these numbers. I resist this, because the only way they get massaged is downward. If a 1000 sq.ft. 2 story space is multiplied times 0.5 it adds 500 "factored sq. ft." to the house square footage. If that is multiplied times a sq.ft. cost of
$100/sq.ft it amounts to $50,000.00. Surely it doesnt add this much to the cost. It probably doesnt, but other areas might add more and if we only reduce the areas that seem too high we will end up with a very optimistic estimate.
When we resist our clients efforts to massage this spreadsheet it has proven to be a pretty good predictor of building costs .
This is a simple Mircrosoft Excel worksheet. Its value is not in its profundity but in its automatic nature. When I do a schematic design I simply plug in the areas and grit my teeth and look at the number it generates. We give it to our clients with the schematic design and reality starts to get injected into the often overheated conceptual design stage of design.
Use this to create your own spread sheet--and when you get factored sq. ft. Ill show in my next article how to use it to create a simple database of your past jobs that will give you some empirical ammunition to explain to your customers why things cost what they do. Clients dont believe architects anyway--they always want to know "what the builder thinks".
|"I have seen builders who, instead of multiplying sq. ft. by a factor, multiply there base cost by the same factors. This gives you the same bottom line, but I think the information is less useful and a bit more prejudicial to you as a builder.
For example, your base sq.ft. price is $100/ sq.ft. and someone has a house of 2000 gross heated sq.ft. Garages, decks etc. add 1000 factored sq.ft. to it. Wouldnt you rather have them go away with the thought that they really have a 3000 sq. ft. house than the thought that you really charge a $150/ sq.ft rather than $100/ sq.ft."
|JOB: Ireton Residence||DATE: 6/14/99|
|AREA||RAW FOOTAGE||FACTOR||FACT SQ. FT.||COMMENTS|
Multiply "Raw Footage" by "Factor" to get "Fact Sq. Ft."
|TOTAL GR HT.||0||2845|
|2 STORY SP||0||0.5||0|
||Screened porch, roof decks, south deck.|
|OPEN DECK||698||0.3||209.4||East & West decks.|
|TOTAL||3708.8||USE THIS FOR COST COMPAR.|
|FROM "HOUSE COSTS - CURRENT"||$118.43||$/ FACTORED SQ.FT.|
|$439,240||YOUR COST AT THIS PRICE|
|Anticipated range of Architectural fees shown as a % of construction cost (for full services) based on our experience. Calculated by dividing total hourly fees by const. cost|
|Lowest||8.00%||$35,139||Multiply 8.00% (lowest) by $439,240 (total cost)|