How to select only bottom face of a ceiling or floor?

[abdelrahmanelfeky6]

hi iam tring to host elements using dynamo using node familyinstance.byFaceAndPoint

but i cant exactly pick the bottom face as seen in picture

the input of Surface.NormalAtParameter is the output of Element.Faces

[Mike.Buttery]

Hi Abdelrahman,

Please take the time to read the following post How to get help on the Dynamo forums

There are many instances of this problem being solved on the forum

Firstly use a Vector.Z node to get the numerical value rather than convert to string, then use approximate equals ‘==’ node (two wavy lines icon) to match to -1

[abdelrahmanelfeky6]

thanks for reply

iam new to the forum and dynamo so may you please provide a photo with the nodes connected

[jacob.small]

As was noted above, this is a common question and answers can be found via search. One such example (for top faces instead of bottom - you’ll have to change a bit of formulas):

Get top face of an element

Hi, the damn special case, although in the question one can suspect the top face of the element (mandatory double filtering to eliminate in the case of inclined beams) [image] cordially christian.stan

[_Vijay]

I think this node is worth exploring for this case.