Because the outer wall's dimension is small with a full two-story house, one can expect better heat insulation and building airtightness.
ご質問ありがとうございます。
"Because the outer wall's dimension is small"＝「外壁の面積が小さいので」
"with a full two-story house"＝「総二階の家では」
"one can expect better heat insulation and building airtightness."＝「断熱性と気密性の向上が期待できる。」
ご参考になると良いです！
アメリカ合衆国 
