**MSC:**- 20E42 Groups with a $BN$-pair; buildings, See also {51E24}
- 20E42 Groups with a $BN$-pair; buildings, See also {51E24}

the Bruhat-Tits-building of the spin group of a quadratic space

over a local number field is introduced and used, to compute the

cohomology of the spin goup of an unimodular lattice of dimension 8

over the ring $\mathbb{Z}[\frac{1}{2}]$ with coefficients in

$\mathbb{Z}[\frac{1}{6}]$. In the first part, the Bruhat-Tits-building

is constructed for quadratic spaces over local fields using

a description by lattices. This description includes the case of

dyadic local fields.