Claim client claim a proportion of decoration costs?

Client is self-employed working from home.  She uses a downstairs room as a waiting room, clients then proceed upstairs to the treatment room.  She has recently redecorated her hall stairs and landing. I can't find any guidance on whether a proportion of these costs would be deductible.  The usual use of home bumpf doesn't seem to address the point where an area is accessed briely en route to another area.  It seems unreasonable to me to claim for the whole percentage that I would apply to the treatment room - I am minded to try to estimate the amount of time that clients spend on the stairs (surely miniscule) and claim accordingly.  Do you all agree?