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SHOB/SHON Confusion


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Hi, peeps,

I've just obtained a PdC to fill in for a potential house purchase. All accommodation on the ground floor, with an unconverted loft above accessed by standard stairs from the hallway. I've worked out the SHOB as total ground floor area x 2 (ground + first floor total). The SHON works out as ground floor area + unconverted loft space (allowing for combles/eaves etc.) Is this correct so far? If so...

Now, the more I read about it, the more confused I'm getting. An example in the PdC shows a garage (SHOB) converted into a lounge (SHON). This implies that the unconverted loft space that I want to use shouldn't be included in the SHON calculation at all yet, and that SHON is currently habitable space (not potential to be habitable as in a loft conversion). I'm creating by transformation SHOB into SHON (PdC 4.5.1 (C)) otherwise eventually the SHON will be larger than the SHOB (illogical).

In summary, is the current SHON the ground floor habitable area, the SHON then increasing when the loft is converted, the two together still being less than the current total SHOB?

Some kind soul help me out here.

Cheers! [B]

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Hi, Derf,

It must be me, but I'm still not getting it. Two floors, the upper unconverted = SHOB. If I take away the eaves and other bits as per the schedule, I'm left with SHON (this is equal to the ground floor + remainder of grenier I want to convert). According to the form, if I now create SHON (the two new bedrooms in the grenier) from SHOB, that floor area is being counted TWICE as SHON, and makes SHON greater than SHOB, which is impossible.

The only way I can see to make it make sense, is to initially only count SHON as current living space, and I don't know if that's correct.

OK - ground floor = 125 sq.m. Unconverted grenier = 125 sq.m. Usable grenier for conversion = 65 sq.m (remainder is low eaves/combles etc.). Therefore SHOB = 250 sq.m. How would you calculate the SHON before and after conversion?

Very many thanks. [B]

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From "Déclaration de Travaux Exemptés de Permis de Construire ou Déclaration de Clôture". Red text is mine.

La surface hors oeuvre brute (SHOB) d'une construction est égale à la somme des surfaces de plancher de chaque niveau de la construction, calculée à partir du nu extérieur des murs du façade, y compris les combles et les sous-sols non aménageables, les balcons, les loggias, les toitures-terrasses accessibles.

La surface hors oeuvre nette (SOHN) est obtenue après déduction de la surface des combles et sous-sols non aménageables, des surfaces on closes, des surfaces de stationnement, des surfaces des bâtiments à usage agricole, des serres de production.

You do not actually "create" SOHN, you deduct an area from SOHB. You can increase the SOHB by adding a new floor (or a new costruction).

If you lay floorboards in an upstairs space, you increase the SOHB, but can deduct this to give the same SOHN as before. If you then add windows, you cannot deduct this area from the SOHB to get the SOHN, as it is now aménageable, so the SOHN is also increased.

If it has a floor but no windows it is not aménageable and should be deducted. If it already has a floor and windows it should already be included in SOHN, and work you are planing on it will not increase the SOHN.



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