Calculating Perimeter / Area ratios to determine u values

heavydawson

Hey all,
I'm trying to calculate my Perimeter / Area ratio for the purposes of determining what thickness of insulation I need in my floors to meet a target U-Value.

It seems like a fairly straightforward calculation, but I've got a couple of questions about it.

1. Does the P/A ratio need to be calculated on a room-by-room basis?
2. If it's calculated on the total floor area (not room by room), should the perimeter value include the lengths of all sides of all walls (internal and external).

The reason I ask is that my P/A ratio based on:
1. Summing the totals of individual room areas
2. Calculating perimeter based on individual rooms (inc. internal and external walls)
, is roughly 1, where it appears most houses are somewhere between 0.4 and 0.7.

Hoping someone can clarify the correct way to calculate this seemingly simple ratio. Thanks in advance!

sydthebeat

Its calculated as a total length on "heat loss" walls, thus internal walls are not considered, this is the DEAP approach anyway which is in accordance with I.S. EN ISO 13370.

also see page 23 here

heavydawson

sydthebeat wrote: »

Its calculated as a total length on "heat loss" walls, thus internal walls are not considered, this is the DEAP approach anyway which is in accordance with I.S. EN ISO 13370.

also see page 23 here

Thanks syd, that brings the ratio back to within expected ranges.